|
|
Register To Post |
| screamin_conure | '92 LT1 idle issues (long post) | ||
|
Senior Guru
 
|
Hi all,
Newb 'Vette owner / Guru member from Northwest Indiana. I posted this over at CAC a few weeks ago, but cabin fever and the need to do something "Corvette" has me wanting to post it here to get a little more input, so here it goes. I have a '92 LT1/A4 coupe with 62k miles. I picked up the car early last fall and to date, I've had the serpentine belt changed, new front seal, new intake gaskets, new IAC valve and TB cleaned, engine smoked for vacuum leaks (none found), new TPS, new air filter, and new PCV valve. I'm now trying to troubleshoot a poor quality idle situation. The car starts every time with the tap of the key (knock wood), but settles into a "bouncy" idle with lots of rich smelling exhaust. My own personal thought/diagnosis is a lean miss at idle due to a faulty or failing injector that's causing the 02 to read lean, thus telling the ECM to pour on the fuel. Being batch fired, there's just too much fuel now at idle and I'm getting the bad smelling exhaust, and an idle that feels "lower" than normal and "bouncy" (I love that term! ). I have an AutoXray EZ-Scan 3000, a fuel pressure gauge, a vacuum gauge and a digital volt/ohm meter. I recently spent an afternoon running a battery of diagnostics on the car and the results are below: Fuel pressure check: I hooked up a FP gauge to the schrader valve and upon turning the key (no engine start), the needle briefly went to 50 while the pump ran for a few seconds and then settled back down to 45. Shut the key off and pressure stayed right at 45 psi. I left it there while I did the cold injector readings, and pressure dropped to around 40 by the time I was done. Started the engine and pressure stayed right at about 42-43 psi. I think I'm good there. Vacuum gauge: I teed a vacuum gauge to the port that feeds the EGR solenoid/ASR line, underneath the driver's side fuel rail cover. Started the engine and vacuum jumped to 15" Hg. Revved the engine a couple of times and vacuum dropped to 0, shot up to about 20, and then settled back down to about 17" Hg. The needle was rock solid stable at idle. I think I'm good there too. Injector resistance check: COLD Cyl. # Ohms 2 12.8 4 13.1 6 13.0 8 12.6 1 12.7 3 12.7 5 12.6 7 12.7 HOT - after a 20+ minute drive where coolant temp hit a maximum of about 225 degrees. Cyl. # Ohms 2 13.3 4 13.1 6 13.1 8 13.3 1 12.9 3 12.9 5 13.2 7 13.3 Road test: Just to be sure it wasn't the MAP sensor, I pulled the connector for it and started the car. It threw a code and SES light for the MAP sensor voltage, but it had no affect on the idle quality/miss. I plugged the MAP sensor back in, cleared the code and started the engine again with the scanner running. Both left and right BLM and left and right integrators were locked on 128 while in open loop. As soon as it went closed loop, the right BLM shot up to 160 and stayed there while the left stayed right around 128, fluctuating only a bit. The right integrator shot up to 180 and was flipping around like mad while the left was right in the normal range. As soon as I drove off, the right BLM dropped from 160 to under 128, and then started to slowly level back off to a more normal range. When I would come to a stop, the right BLM would just climb right back up to 160 and the low/bouncy idle would return. The whole cycle would repeat with every movement in traffic and every stop. Right 02 sensor readings were all over the place (from 200 mV up to 800+ mV), while the left sensor, while varying, seemed to be ranging more in the 450 mV range. At no point that I was able to see, did the EGR duty cycle move off of 0%. I thought that was kinda' strange. TPS voltage was bang on at .62 volts at zero throttle and ranged normally with throttle input. When standing near the idling engine on the passenger side of the car with the clamshell open, I can also hear a clicking of sorts. It's not really the metallic-sounding tap of a bad lifter, but more of just a rythmic mechanical clicking. Driver's side sounds fine. As I've mentioned, even though the resistance readings are normal and the fuel pressure holds well, I'm still about 85% convinced that I have a bad injector somewhere on the passenger-side bank. The other 15% of me thinks it could possibly be the right 02 sensor. Thoughts? Thanks in advance! Ron |
||
Posted on: 2010/1/28 20:32
|
|||
 Transfer
|
 
|
||
| TommyT-Bone | Re: '92 LT1 idle issues (long post) | ||
|
Chair-man of the bored
 
|
What condition are the plug wires, plugs, cap etc.? Checked for a light show at night? Hang around. Support is on the way.
|
||
Posted on: 2010/1/28 20:51
|
|||
|
Transfer
|
|
||
| BillH | Re: '92 LT1 idle issues (long post) | ||
|
The Stig Moderator
 
|
Welcome aboard.
The rich smell and the bouncy throttle may not be connected, my 92's always a tad rich in open loop, but no idle problems. Have you double checked the AutoXray against the dash for codes? Nothing against AutoX, I have an ODB2 one but, I have seen a couple 92-93s that had nothing on a reader but codes came up on the dash. FP looks fine, Vac too. Injectors look OK but, remember, you're just checking the coils, not verifying good spray. If you're confident that one bank's causing it, you could switch the injectors side to side. I don't think it would be the IAC but, did you check pintle lenght and do the new valve startup procedure? I'm inclined to agree that it may be the 02. If the sensor is going open at temp, it will cause everything to go back to open loop. I hate to throw parts at problems but 02 sensors are inexpensive. The 02 will throw a Code 13 (H13) in module 4.1 if it's doing this. Reading the codes on the dash is in our tech section if you've never done it. Good Luck |
||
Posted on: 2010/1/28 21:02
|
|||
|
_________________
Every man dies but not every man lives. |
|||
|
Transfer
|
|
||
| 1Fast04Vert | Re: '92 LT1 idle issues (long post) | ||
|
Elite Guru
 
|
I am agreeing with you, bad injector. Try contacting Jon at FIC. He has is own forum on here, excellent knowledge and customer service, and great prices on the Bosch III.
Then again the ticking could be a plug wire shorting out, even the very rare cracked plug insulator. |
||
Posted on: 2010/1/28 21:04
|
|||
|
_________________
2004 Vert. 475hp. Built by Vengeance Racing |
|||
|
Transfer
|
|
||
| screamin_conure | Re: '92 LT1 idle issues (long post) | ||
|
Senior Guru
|
Quote:
Good thought. I didn't think about checking for arcing. I forgot to mention that I also had a new water pump and t-stat installed as well. Even though the original wasn't leaking, my mechanic (another 'Vette Nut who I found the car through) recommended a new water pump to avoid any potential leaks and resulting dead Opti down the road. He checked the Opti at the time he changed the pump, and said it looked ok, though he was pretty certain it's the original. Plugs are on the agenda a bit later in the season. However, wouldn't an ignition/plug/wire problem manifest itself on acceleration or under load? The car accelerates hard and cruises smoothly. |
||
Posted on: 2010/1/28 21:06
|
|||
|
Transfer
|
|
||
| screamin_conure | Re: '92 LT1 idle issues (long post) | ||
|
Senior Guru
|
Quote:
Thanks for the reply Bill! No, definitely no codes. None from the AutoXray and none from jumping terminals A and G with a paperclip. The IAC was replaced shortly after I got the car to correct a way-too-high idle situation at the time, and yes, I've done the IAC reset proceedure at least twice. That's the thing; I'd hate to throw money at it too, and a new 02 sensor is way less expensive than new injectors. However, with everything that I've read on the original Multecs from that time period, I'm really dubious of them. |
||
Posted on: 2010/1/28 21:11
|
|||
|
Transfer
|
|
||
| screamin_conure | Re: '92 LT1 idle issues (long post) | ||
|
Senior Guru
|
Quote:
If I decide to go with new injectors, Jon will definitely be the guy I call! |
||
Posted on: 2010/1/28 21:14
|
|||
|
Transfer
|
|
||
| screamin_conure | Re: '92 LT1 idle issues (long post) | ||
|
Senior Guru
|
"If you're confident that one bank's causing it, you could switch the injectors side to side."
Yes! Didn't think of that either. That'd tell me for sure if I'm dealing with an injector. It would be a bit of work, but it would tell me for sure if my $169.00 would be going to good use. |
||
Posted on: 2010/1/28 21:18
|
|||
|
Transfer
|
|
||
| BillH | Re: '92 LT1 idle issues (long post) | ||
|
The Stig Moderator
|
My 92 injectors are origional at 87k mi. I balanced a nickel on the motor at idle the other day. Not saying yours could not be bad.
If your wires are origional at 62k, they're close to being shot. Are they black with white numbers? I ohmed mine at 64k and they were way up there, replaced with Taylors (highly recommended) and NGK TR55 plugs. If your plugs are old (and are AC Delco) the platinum tips are noted for going away. Taylor wires (at Summit) are about $70, fit perfect and will outlast stock by 2X. |
||
Posted on: 2010/1/28 21:20
|
|||
|
_________________
Every man dies but not every man lives. |
|||
|
Transfer
|
|
||
| BillH | Re: '92 LT1 idle issues (long post) | ||
|
The Stig Moderator
|
BTW, the ticking, mine does it. I don't worryabout it anymore.
There was also a TSB on ticking, check the nots that hold the heatshields to the exhaust manifolds. |
||
Posted on: 2010/1/28 21:23
|
|||
|
_________________
Every man dies but not every man lives. |
|||
|
Transfer
|
|
||
| Woodstock | Re: '92 LT1 idle issues (long post) | ||
|
Senior Guru
|
Sounds like the O2 sensor to me.
If you can read out the left and right bank separately you should have two O2 sensors. You could switch those two sensors as well, to see if the problem moves along. |
||
Posted on: 2010/1/28 21:47
|
|||
|
_________________
91 convertible |
|||
|
Transfer
|
|
||
| screamin_conure | Re: '92 LT1 idle issues (long post) | ||
|
Senior Guru
|
Thanks again Bill! While I can see that the age and mileage of the plugs and wires would dictate replacement, would they necessarily be the cause of, or contributing factor to, the wild swings in BLM on the right bank?
|
||
Posted on: 2010/1/28 21:50
|
|||
|
Transfer
|
|
||
| BillH | Re: '92 LT1 idle issues (long post) | ||
|
The Stig Moderator
|
Quote:
No. The plugs and wires are just a maintainence item like batteries and brakes. |
||
Posted on: 2010/1/28 21:57
|
|||
|
_________________
Every man dies but not every man lives. |
|||
|
Transfer
|
|
||
| screamin_conure | Re: '92 LT1 idle issues (long post) | ||
|
Senior Guru
|
Hey, thanks for all of the help everyone! After the weather warms up a bit, and before I shell out the $$ for a new set of injectors, I'm going to try swapping sides on the stock injectors and see if my problems move over to the left bank. I really think that's where my bad idle/lean miss/rich exhaust problem is.
After that, I'll be looking to replace 02 sensors, plugs and wires a bit further down the road. Regards, Ron |
||
Posted on: 2010/1/28 22:37
|
|||
|
Transfer
|
|
||
| tjpreul | Re: '92 LT1 idle issues (long post) | ||
|
Elite Guru
 
|
There are several items for this condition to check. A few more from the FSM that won't cost. EMC grounds or fuel in pressure regulator hose.
|
||
Posted on: 2010/1/29 0:29
|
|||
|
_________________
Vegas wasn't built on winners. '92 auto, MSD, Banski, Taylor wires, SS lines, C5 rims, 3.07 gears, white gauges, seats from a '96. Motor: Forged rotating assy, Probe pistons, CC valvetrain, AFR heads, Procharger P1SC |
|||
|
Transfer
|
|
||
| bogus | Re: '92 LT1 idle issues (long post) | ||
|
Grand Imperial Pooh-Bah
 
|
Ron,
Welcome aboard! How much does the idle wander? You see, the opti will cause that. Is there a high RPM miss? IF so, the opti will cause this, too. The opti has one weakness - moisture. The waterpump leaks on it, and coolant gets in, causing carbon tracing. Then comes the war... the engine controller is fighting a battle with the dreaded miss. When the tracing gets bad enough, it will cause a miss at idle. The computer compensates for it by retarding the timing. The miss clears and the timing sets back to spec, miss returns, the circle jerk continues. Is it the original opti? If so, I would be very suspect of it. If time hasn't killed it, mileage will. |
||
Posted on: 2010/1/29 4:01
|
|||
|
_________________
The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
|||
|
Transfer
|
|
||
| pr0zac | Re: '92 LT1 idle issues (long post) | ||
|
Elite Guru
|
if one o2 isn't moving around its dead.. replace it and post results. it should be cycling back and forth when in closed loop. if its staying in one area and not changing when reving the engine its bad.
|
||
Posted on: 2010/1/29 4:23
|
|||
|
_________________
96 lt4. 357ci, 11:1, LE 226/232, LE2 LT4 heads, ported LT4 intake, EM Gladiator44, EM LT's, stock exhaust, NX kit. |
|||
|
Transfer
|
|
||
| screamin_conure | Re: '92 LT1 idle issues (long post) | ||
|
Senior Guru
|
Quote:
I did pop the vacuum line from the FPR and gave it a sniff. No gas smell. I'll have to dig out my FSMs and find out the proceedure for checking the ECM grounds. Thanks for the tip! This is an awesome forum!  |
||
Posted on: 2010/1/29 15:48
|
|||
|
Transfer
|
|
||
| screamin_conure | Re: '92 LT1 idle issues (long post) | ||
|
Senior Guru
|
Quote:
Actually, both are moving. It's just that the right one, where I'm seeing the high BLMs, is moving around in a much wider range than the left. Both sensors appear to be responding normally, which is why I'm so very suspect of the injector(s). |
||
Posted on: 2010/1/29 15:50
|
|||
|
Transfer
|
|
||
| BillH | Re: '92 LT1 idle issues (long post) | ||
|
The Stig Moderator
|
Quote:
There's no real procedure for checking grounds. While the 92s are supposed to have some problems with grounds, I've never had one. But, for piece of mind, I've disconnected most, wirebrushed the frame and connector and reinstalled with stuff to prevent oxidation (I use Vasoline, been doing it for years including batt terminals). All the grounds are on page 8A-203-0 in your FSM. |
||
Posted on: 2010/1/29 16:40
|
|||
|
_________________
Every man dies but not every man lives. |
|||
|
Transfer
|
|
||
| screamin_conure | Re: '92 LT1 idle issues (long post) | ||
|
Senior Guru
|
Quote:
Hey, thanks Bogus! This is a really great forum. Well, the last time I had the car out a couple of weeks ago, it didn't exhibit the "low" idle that it was prone to last fall before I put it away. When I say "low", the tach needle would drop a bit below 500 rpm and at the time I did not have my scanner so I'm just going by what I saw on the tach and what I felt in the seat of my pants. When it did this, the car shook pretty good and felt as though it was going to die, but never did. This time around, the measured idle and the desired idle were pretty darn close (within 25 rpms). It's just that I'm getting the slight rythmic bounce at idle, the high right BLM, and a rich smelling exhaust. It will, on occasion when coming to a stop after cruising, idle a bit high at around 750 - 800 rpm, but will quickly come back to normal idle after sitting there and holding the brake for a few seconds. There is no high RPM miss at all. The thing pulls like a monster under WOT, and steady cruising at any speed is smooth. I'm sure the Opti is original. The next time I get the car out on the road with the scanner, I'll have to double-check the timing readings. I can see where improper/incomplete ignition can mess with 02 output, but if it were the Opti wouldn't I be seeing issues on both banks rather than just one? |
||
Posted on: 2010/1/29 16:42
|
|||
|
Transfer
|
|
||
| screamin_conure | Re: '92 LT1 idle issues (long post) | ||
|
Senior Guru
|
Quote:
Thanks Bill! |
||
Posted on: 2010/1/29 16:44
|
|||
|
Transfer
|
|
||
| bogus | Re: '92 LT1 idle issues (long post) | ||
|
Grand Imperial Pooh-Bah
|
Quote:
The way the opti is put together, bank-to-bank error wouldn't surprise me. All the plug ports on the cap are on the respective side of the engine!! Thanks for the kind words! Hope you enjoy the place!!!  |
||
Posted on: 2010/1/29 17:45
|
|||
|
_________________
The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
|||
|
Transfer
|
|
||
| screamin_conure | Re: '92 LT1 idle issues (long post) | ||
|
Senior Guru
|
I have a little update on progress here...
Last week, my mechanic replaced both 02 sensors and the inline fuel filter. Got the car back and it ran slightly better than before (idle was slightly smoother). I had the scanner hooked up directly from the mechanic's shop, and with the new 02 sensors, both BLMs were in the 110-115 range at idle and 120-125 under acceleration/driving. I could actually see both 02 sensors neatly flipping between lean/rich whereas before the sensors would go in one direction (typically rich) and stay there for a long moment, and do a lot of really fast flipping around. I immediately took it for an emissions test and it passed with flying colors. Always a good thing! As I had mentioned in my original post, the actual RPMs at idle and the "Desired Idle" as asked for by the ECM were very close and consistent. Now, this past Saturday, I installed a set of Bosch III injectors from FIC. Easy enough job, and it went off without a hitch. I was VERY careful to check for leaks (none found). Fuel rail bolts torqued down to spec. Everything looked good. The car took a bit of cranking to fire, as expected. Here's were things are getting confusing though. The idle, though noticeably smoother with the new injectors, no longer wants to stay at a consistent RPM. In other words, once up to operating temp and in closed loop, the desired idle and actual RPMs are almost always off. Most of the time the actual RPMs are much higher, but sometimes lower. Driving the car like this results in a different idle experience at almost every stoplight. Sometimes, as I'm applying the brakes approaching a light, I can really feel the transmission laboring against the motor as it is downshifting, and sure enough when I get to a stop, I need extra pressure on the brake pedal to keep the car still. Other times, I'll come to a stop and the tach needle will drop slightly below the 500 mark and whole car will vibrate. Yet, other times, it will come to a stop and idle just fine. It's no fun at all driving the car in this state, and I also know that when it's idling high, I'm putting a LOT of additional wear and tear on my trans and brakes. Now, last fall, before storing the car for the winter, I had installed a new PCV valve. I bought one of the $1.65 cheapy valves from the major auto parts chain near my house. From everything that I've read about PCVs, my symptoms really sound like they COULD be PCV related, and I have a suspicion that my el-cheapo PCV might be the source of my grief. Thoughts? This coming weekend, my brother and I are planning to check over all the vacuum lines, pull the TB off and thoroughly clean it, focusing on the IAC passage way and put it back on with new gaskets. We're also putting in a fresh set of plugs, and I also have a new ACDelco PCV valve on order as well. Fingers crossed. |
||
Posted on: 2010/3/16 20:25
|
|||
|
Transfer
|
|
||
| Tre57 | Re: '92 LT1 idle issues (long post) | ||
|
Senior Guru
|
I'm reading this with great interest. My 93 is doing similar things. Once it's good and warm it idles too low. (below 500 rpm) Sometimes it wants idle too high but just momentarily... like you, I have apply a lot of brake when it does this. Plugs and wires are in great shape, original injectors and opti. The fuel pump is also new. It doesn't feel or sound like it has a miss... just low and rough. Runs great @ cruise, part throttle acceleration, and WOT.
Starting to think it might be white and red color combo. LOL Good luck! I will let you know if I make any progress with mine. |
||
Posted on: 2010/3/17 7:42
|
|||
|
_________________
93 AT Coupe |
|||
|
Transfer
|
|
||
| screamin_conure | Re: '92 LT1 idle issues (long post) | ||
|
Senior Guru
|
Well, with the cold crappy weather today, we cancelled our plans to install new plugs, but I think, I THINK, I may have things sorted out just the same (fingers crossed).
As I mentioned in my earlier post, I was a little suspect of the aftermarket PCV valve that I had put in last fall. I went ahead and bought a new AC Delco valve and popped that in this afternoon. I HAD ALSO PUT THE ORIGINAL THROTTLE POSITIONING SENSOR BACK ON. I had changed it out last fall for no real reason other than it was a cheap/easy job to do, and MAY have corrected my original idle issues. I put the original back on for the same reason I put in an AC Delco PCV; I was a little suspect of the aftermarket Borg Warner part. The first thing I noticed with the original TPS back on, is that it reported .62 volts at idle on the scan tool, where the Borg Warner unit had reported .64 volts. I started the car and let it sit and come up to temp. Idle seemed just a tad low at first, but by the time I got my scanner hooked up, it had come up a bit. Desired idle and actual RPMs were now bang on (within 25 RPM). Despite the cold, wet, slick roads, I headed out for a little road test. Its nasty here today, around 35 degrees and sleeting, and the car seemed just a little stumbly at first. As I drove around though and the engine became warmer, things started to smooth out. I kept an eye on the desired idle reading on the scanner, comparing it to the actual RPM readout at each stop sign. For the most part, they stayed within 100 RPM or so of each other, with the actual RPMs erroring toward the high side. At no time did it idle so high so as to require intense pressure on the brake pedal at a traffic light. If it hadn't been for the lame weather, this would have been a very enjoyable ride! With the new injectors, 02 sensors, a good PCV valve, and the original TPS back on, the car ran, and idled, about as well as an 18 year old LT1 might be expected to. I think the two lessons learned here are, first, don't just swap out a part on a hunch, and second, stick with genuine OEM parts. From now on that's all my baby is getting! Cheers! Ron |
||
Posted on: 2010/3/21 0:05
|
|||
|
Transfer
|
|
||
| Tre57 | Re: '92 LT1 idle issues (long post) | ||
|
Senior Guru
|
Awesome! Good to hear errr..... read
 |
||
Posted on: 2010/3/21 21:14
|
|||
|
_________________
93 AT Coupe |
|||
|
Transfer
|
|
||
| Matatk | Re: '92 LT1 idle issues (long post) | ||
|
Webmaster
 
|
Quote:
I always prefer to use OEM sensors when available. Glad you got it worked out  Matthew |
||
Posted on: 2010/3/21 23:32
|
|||
|
_________________
2002 EBM convertible, Magnusson supercharger, cam, headers, etc. 1989 Corvette...RIP |
|||
|
Transfer
|
|
||
| screamin_conure | Re: '92 LT1 idle issues (long post) | ||
|
Senior Guru
|
Well, back to the drawing board.
I've been putting some miles on the car since my last post and the driveability issues continue. Despite having replaced the IAC last year with a new AC Delco unit, I really, REALLY thought that I would cure this problem once and for all my removing the throttle body and giving it a good cleaning, which is what I did this past weekend. When I put it back on, you could almost see your reflection in the blades! I removed the IAC and didn't mess with the tip or anything, just laid it aside while I cleaned the TB. I gave special attention to the IAC passage too. Clean as a whistle now. I put everything back together with a new gasket. The car STILL doesn't want to idle quite right. It starts fine when cold, idles higher as it should when it's cold and drops down to around 550 RPM in gear within a minute or so, but as the engine continues to build heat, the idle RPMs in Drive begin to creep back up to around 650. Not TOO bad, but not what the ECM is calling for (550). Now, yesterday I took it out for a fairly spirited ride and was having a bit of fun with her. It was fairly warm here yesterday, around 85 degrees. After the ride, I brought it home and parked it in the garage. Went back out with my wife for some dinner about 20 minutes later and here is what happened: Starting took a few extra cranks. When it finally started, the tach needle started low (around 450), jumped to around 1100, fell back to around 500, jumped back to 1100, fell back to 500, back to 1100 and then back to 500 and then stayed there. All of this happened within just a few of seconds. Drove to dinner, just a few blocks away and parked. About an hour later, came back out, started it, and now it's idling at 1,500 RPMs in park. Had to drive home like that and litterally never touched the accelerator pedal the entire way home. Parked in the garage, shut it down, restarted, still high. Shut it down for a few minutes longer and grabbed a trouble light to take a look see. Started again and now it's a bit lower, around 1,100 RPM in Park, but still high. I left it running while I was poking around under the hood, desperately trying to listen for the hiss of a vacuum leak, when slowly, gradually, the idle comes back down to around 650 in Park. W. T. F.?? I'm seriously starting to think this isn't air/fuel delivery anymore and more likely an Opti/ignition thing. I've been reading here and there how heat can affect an Opti living on borrowed time, and how the carbon tracing effect can cause wild fluctuations in idle. Time to break out the FSM again and start looking at ignition troubleshooting flow charts. I love this car! ;) |
||
Posted on: 2010/4/15 21:46
|
|||
|
Transfer
|
|
||
| screamin_conure | Re: '92 LT1 idle issues (long post) | ||
|
Senior Guru
|
And in looking back over this thread, more than a few people have mentioned the Opti, plugs, wires, etc.
 Stupid newbies; never listen do they? ;) |
||
Posted on: 2010/4/15 22:01
|
|||
|
Transfer
|
|
||
| flyboy | Re: '92 LT1 idle issues (long post) | ||
|
Elite Guru
|
Could this not be the Idle Air Control cutting in and out?
|
||
Posted on: 2010/4/15 23:24
|
|||
|
_________________
'91coupe, LT4Hotcam, some other stuff. If it's too loud, you're too old. "He works on old cars, then junks 'em" |
|||
|
Transfer
|
|
||
| screamin_conure | Re: '92 LT1 idle issues (long post) | ||
|
Senior Guru
|
Since I dislike posts with no real resolution as much as the next person, I thought I'd post an update on my progress.
All summer long, I continued to experience the same driveability issues as I had been. Namely, a poor quality, surging idle. The car would start normally, idle fairly rough, smooth out as it warmed up, but would eventually continue to rise to the point where I would come to a stop at a traffic light with the engine idling at 800 - 900 RPMs in gear. In June, I discovered that the new 02 sensors that I had installed back in March were wreaking havoc with my ECM. The ECM threw a code 63 (right 02 circuit fault) several times, and a code 44 (left 02 lean) once. I finally got around to taking it back to the mechanic who did the 02 sensor install and he found the right 02 to be bad and replaced it. A week later, another code 63. In watching the 02 voltages on my scan tool, the right sensor was just hovering around 450 mV with only slight changes. The left was flipping from lean to rich, but as soon as you would tip in the throttle, the voltage would drop to 20 - 40 mV and stay there. In addition, the car simply would not go into closed loop, even after 20 minutes of driving. Only a blast of WOT would get it into closed loop, but it would revert back to open loop a few moments later. These were genuine AC Delco AFS22 sensors. I had come across a thread on another non-Corvette forum where a number other folks were having similar issues with the same sensor. I ordered up a pair of Denso 234-1001 sensors and have been running these now for more than two weeks and so far, my 02 sensor issues are gone. The ECM now goes into closed loop within just a few minutes of starting the engine, and the sensors on both sides flip nicely between 900 mV and 100 mV. The car now ran noticeably better, but I still continued to have the surging idle. The same day that I had the Densos installed, the SES light came on again. This time it was a code 32 (EGR failure). I had tested the EGR system previously according to the charts in the FSM and everything looked ok. But, I figured that since the EGR components were 18+ years/64,000 miles old, I'd go ahead and replace them anyway. Started with the solenoid; no more code 32, but the surging idle remained. Just yesterday, I replaced the EGR valve itself and I'm happy to say that my initial road test resulted in no surging idle! Idle is still a bit rough when the engine is cold, but not as rough as before and smooths out VERY nicely once up to temp. Idle RPMs were 600 - 625 RPMs in gear, at a stop. Still higher than what the ECM is calling for (550 RPMs), but the car is MUCH more driveable. Looking to put some more miles on it this week. Fingers crossed that it stays this way! Ron |
||
Posted on: 2010/8/29 19:57
|
|||
|
Transfer
|
|
||
| screamin_conure | Re: '92 LT1 idle issues (long post) | ||
|
Senior Guru
|
A little more good news...
Just came back from a 75 minute, 35+ mile, combined local/rural/expressway cruise and at no time did the idle at a traffic stop exceed 650-675 RPMs, in gear. A drive like this would have produced all kinds of histrionics from my idle previously. Before, I would have felt the engine and transmission fighting each other as I would brake to a stop. Very little to none of that now. Also before, there would be times when I'd be able to take my foot off the accelerator and the car would continue to drive itself at speeds of up to 25 - 30 MPH. Now, it just begins to slowly decelerate. About the only real issue that I noticed was when I left the garage at the beginning of the trip. The car was idling very low and rough; 350 - 450 RPMs and actually threatened to die at the first few stop signs. It was also fairly herky-jerky accelerating away from those same stop signs. It took a good 15 minutes of stop-and-go driving before the idle finally came up to a more normal level and acceleration began to smooth out. This was the only the second time that I drove the car after having the battery disconnected for an hour or so yesterday while I changed out the EGR valve. It did it the first time I took it out yesterday too. I'm hoping this is just the ECM relearning things and not a new issue. |
||
Posted on: 2010/8/29 22:40
|
|||
|
Transfer
|
|
||
| bogus | Re: '92 LT1 idle issues (long post) | ||
|
Grand Imperial Pooh-Bah
|
Short of a retest of the cold start, it sounds like yhou have made great progress!!!
I hope the cold start issue fixes itself... |
||
Posted on: 2010/8/30 6:22
|
|||
|
_________________
The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
|||
|
Transfer
|
|
||
You can view topic.
You cannot start a new topic.
You cannot reply to posts.
You cannot edit your posts.
You cannot delete your posts.
You cannot add new polls.
You cannot vote in polls.
You cannot attach files to posts.
You cannot post without approval.
|
|