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This is the manual transmission from 1984-1988.

It’s a Borg-Warner Super T-10 with a planetary overdrive attached to the tail shaft housing.
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CorvetteBob Hunting Idle, stalling
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For a number of years, my car has had a hunting idle w/ stalling as part of its personality, but I can't deal with it any more.
This started BEFORE any mods were made.
When cold, I'll back out of the driveway and it'll die when I take my foot off the gas. hot or cold, but not with any pattern it'll die when I come to a light or other stop. When getting off the highway and stopping at the exit, it might die. Sometimes, instead of stalling, it'll just drop into the 300's range and then work it's way back to the hunting 700-900+ idle range. So here's what I've done so far;

Last year I put on a new IAC. It seemed to help, but not for long.

Tonight I checked my TPS and it was at .55 volts. I reset it to .61. I didn't think it would do much, but it's free and worth a try.

I've got one of those super duper things you put into your throttle body to smooth out the incoming air. Last year I took the fastener for it out and smoothed it way down in case it was restricting air into the IAC passages. Is it possible that could be restricting air from the IAC and causing some of these problems"?

It's been a while, but the last time I checked my fuel pressure, it was around 43-44 lbs.

I "think" I read somewhere that for some cars, removing the MAF screens can cause these types of problems. A few weeks ago, I put my incoming screen back onto my MAF. Nope.

Thanks for reading, if you can offer some help, I'd appreciate it.
Posted on: 2011/7/15 5:28
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BillH Re: Hunting Idle, stalling
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Bob, I haven't played much with L98s but this sure sounds like an IAC thing. On an LT1, when you put in a new one, there's a reset procedure.
It sounds like either an intermittent electrical signal to your IAC or the IAC passages plugged.

have you ever had the T/B off and cleaned it, blew out the vacuum passages, etc?

It's not a fuel pressure thing.
Posted on: 2011/7/15 13:07
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Matatk Re: Hunting Idle, stalling
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Why did you reset the TPS to .61? As far as I recall it should be .54-.56.

When was the last time you removed the TB, disassembled, and cleaned it?

Also, any vacuum leaks?

Matthew
Posted on: 2011/7/15 13:22
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Matatk Re: Hunting Idle, stalling
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Sorry I got sidetracked with the kids, Bill posted basically the same thing as me.

Have you done the IAC/tps/min idle speed reset?
Posted on: 2011/7/15 13:23
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CorvetteBob Re: Hunting Idle, stalling
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THanks for the help guys....

When I put the new IAC on I took the throttle body off and went thru and cleaned it then. that's when I reduced the size of that fastener that holds onto the air thing in my tb. When I put it back together I thought I followed the procedure to reset it, but I coulda plucked that up. How do you guys do it, I'll try it again.

Have I done the IAC/tps/min idle speed reset? I'm not sure what that is. I know I sound like a newb here, but I'm afraid I'm one of the old schoolers that needs to catchup.

I know the TPS sweet spot is .54-.56, I just was wondering. No biggee, I'll put it back. I did notice, that my fsm says the TPS reading shoud be around 5.0 when wide open. Mine only goes up to 3.2-3.6 . Obviously, that's low, could that be part of the problem?

Vacuum leaks? Thats certainly possible with a Superram, but this did NOT get worse when I put it on. If I disconnect and isolate the engine from the external vacuum can, etc., will that make it run worse or can I use that as a way to determinie that there's a leak in the evap system?

Now to check out HCF.......
Posted on: 2011/7/15 15:47
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CorvetteBob Re: Hunting Idle, stalling
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I was able to secure a new Borg-Warner TPS and swap it over.
I know, I was trying to avoid just replacing parts, but I thought it was worth what I paid. During the swap I foound out why my TPS reading only went up to 3.25, it's because the hose clamp for the air intake bellows was blocking the throttle from opening all the way.
Now the closed position reading is back at .56 and at WOT it goes up to 4.54. Better, but not the 5.0 as the FSM sez it should be. I started the car up and now it seems better, but still wants to die if I goose the gas, especially with the AC on. While sitting in the garage, I ran the RPM up to aboout 2500 and I noticed that even as I held the pedal still, the RPM would try to "hunt" between 2400-2500 and sometimeds a bit more or less.
What do you guys think?
Posted on: 2011/7/16 5:34
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CorvetteBob Re: Hunting Idle, stalling
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Another update!!!!!!!!!

I went online looking for the procedure for the IAC/tps/min idle speed reset, and got pretty close. But after the 2nd or 3rd time of it not quite getting there, I happened to finally find it in my FSM. It added a couple of key pieces of info. 1st, it told me when to remove the ground between the A/B connectors on the ALDL. 2nd, and most importantly, it told me to unplug the inline connector for the ESC module, and when to do it! So now it's 5am Saturday morning and I'm due to be up at 8:30, so I hafta hit the hay. I'll let you guys know if things are better for sure, or if I hafta dig in and start looking for vacuum leaks.
Posted on: 2011/7/16 9:03
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TommyT-Bone Re: Hunting Idle, stalling
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Keep up the good fight Bob. Your bound to have a revelation.
Posted on: 2011/7/16 11:38
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Matatk Re: Hunting Idle, stalling
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Bob - as far as the TPS, the 5v is the reference signal, it should see around 4.6v at WOT off the top of my head.

I was going to post the IAC reset procedure, I've got it in a few other posts - try this:

Photobucket

Hopefully you solved the problem, though. Keep us posted.

Matthew
Posted on: 2011/7/16 12:01
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CorvetteBob Re: Hunting Idle, stalling
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Quote:

Matatk wrote:
Bob - as far as the TPS, the 5v is the reference signal, it should see around 4.6v at WOT off the top of my head.

I was going to post the IAC reset procedure, I've got it in a few other posts - try this:

Photobucket

Hopefully you solved the problem, though. Keep us posted.

Matthew


Thanks for the procedure Matt. I already printed it off. It's close to the one I used, but I hooked my voltmeter to the Red and Black wires of the TPS, not Black and Blue.

I didn't thnk to check my timing. If I remember right, I set it at 10* BTC, but it's been a while, so I really can't say for sure.

I didn't do no.11 exactly, but I did let it run a good while.

Today when I went to start it, it started fine, but then as I was backing down the driveway I let off the gas and it died. It started right back up, but that's the only hitch I've seen so far. I do have a feeling the driveability is better, but that's subjective.

I'll be back after more driving.
Posted on: 2011/7/16 19:06
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Matatk Re: Hunting Idle, stalling
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I'd reset the timing to 6* btdc and see if that helps. You'll really need a good scan to read sensor values when it's stalling.

Matthew
Posted on: 2011/7/17 0:07
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CorvetteBob Re: Hunting Idle, stalling
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The timing is now 6* BTC.

I set it to 6* after I got home from work. It was on 4*.(???)
I waited to see if things were any better the way it was. Drivability is definatly better. It still stalled when 1st backed down the driveway. There's one place I can usually expect it to die in traffic on my way to work, and it did.
When I get off the highway and turn into traffic (whether or not I hafta stop for the light) I then accelerate, and shift. If the next light turns and I hafta stop, it dies.

Another note, after setting the timing tonight, I revved it and held steady at 1600. With a steady foot on the pedal, the engine speed alternated from 1600-1700RPM every several seconds. I also tried holding a steady pedal at 2200 RPM and it not only did the same thing from 2200-2300+, but I could feel the pedal seemingly "fall out" from under my foot, then come back as the engine speed fluctuated.
Could there be something goofy causing the EGR valve to cycle, letting in too much "air"?
Posted on: 2011/7/18 4:42
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Matatk Re: Hunting Idle, stalling
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I guess theoretically it could be an EGR problem. Or MAF, or TPS, IAC, or anything else that monitors or meters air intake. Could also be a vacuum leak as we discussed. Could be on a component you didn't replace with the superram swap...for example the brake booster or booster line, hard plastic vacuum lines have a crack, etc. Vacuum leak is what I'd look for first.

Matthew
Posted on: 2011/7/18 11:38
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BillH Re: Hunting Idle, stalling
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Quote:

CorvetteBob wrote:
Another note, after setting the timing tonight, I revved it and held steady at 1600. With a steady foot on the pedal, the engine speed alternated from 1600-1700RPM every several seconds. I also tried holding a steady pedal at 2200 RPM and it not only did the same thing from 2200-2300+, but I could feel the pedal seemingly "fall out" from under my foot, then come back as the engine speed fluctuated.
Could there be something goofy causing the EGR valve to cycle, letting in too much "air"?


Very doubtfull Bob. Do the TPI motors have a solenoid on the EGR? Even if they do, I'd bet big bucks that the EGR isn't the problem.

I think you need to find a shop with a scope and do the above.
The engine speed should be rock steady (as steady as your foot can make it anyway).

There's only 2 things that can cause the above, spark or fuel. A scope will tell you if anything's going on with the spark. Fuel- probably not a fuel pressure thing but could be injector imbalance. How many miles on your injectors?

How old are your oxygen sensors?
Posted on: 2011/7/18 13:05
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CorvetteBob Re: Hunting Idle, stalling
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I guess I'll start loking for a possible vacuum leak. Talk about a "target rich environment".

Bill, Im not sure where to take it around here. There's one small shop across town, but I don't care for the neighborhood they leave the cars out in everynight. The dealers won't even look at something that's been modified. If they do, they immediately label the mod as "the problem" and send it home.
Posted on: 2011/7/18 15:51
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BillH Re: Hunting Idle, stalling
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You may have to go out of town, Bob.
You'll have to find a shop that has a scope, I'd think that if you could make an appointment, it wouldn't take longer than an hour. Just hook it up and run it like you described.

While it may not be spark, putting it on the scope would eliminate the electrics as part of the problem (or pin point it as the problem).

You're in "this is a bitch" situation.

I don't think it's vacuum but you have to check.

Gotta ask again, how old are the injectors & oxy sensors?
Posted on: 2011/7/18 16:18
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CorvetteBob Re: Hunting Idle, stalling
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I think I replaced the oxy sensor with the header install a couple years ago. It came from NAPA, a trusted source around here. The injectors are the OEM units, but were cleaned individually when out for my 1st manifold swap several years ago when I put on the Accell base. I religiously use STABIL in my gas to keep it from gumming up, but I suppose I'm gonna hafta take the SR apart and have them cleaned again.
Posted on: 2011/7/18 18:11
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TommyT-Bone Re: Hunting Idle, stalling
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Info

Posted on: 2011/7/18 19:36
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josephf31 Re: Hunting Idle, stalling
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I read this whole post and nowhere have I seen anyone mention the fuel filter? It could be a SWAG but it's been known to cause numerous 'issues', especially if it's not a high quality one like a WIX etc. (not junk like FRAM). My $.02 :-)
Posted on: 2011/7/19 3:39
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CorvetteBob Re: Hunting Idle, stalling
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Thanks for the video! Using that method, I was able to determine that 2 of my injectors checked at 17 ohms, 4 at 18, and I was unable to get to the other two because of the SuperRam. Is there a way I can check the other two thru the connector?
Posted on: 2011/7/19 3:59
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CorvetteBob Re: Hunting Idle, stalling
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Quote:

josephf31 wrote:
I read this whole post and nowhere have I seen anyone mention the fuel filter? It could be a SWAG but it's been known to cause numerous 'issues', especially if it's not a high quality one like a WIX etc. (not junk like FRAM). My $.02 :-)


The FF that's on it just might be a FRAM. It's only a couple years old, meaning less than a 1000-1500 miles.
It bears looking into, but lets all remember, like I stated at the start, the cars' behavior has been like this since the '90's. I'm just now getting to where I'm sick of the problems it creates.
Posted on: 2011/7/19 4:34
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Matatk Re: Hunting Idle, stalling
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CorvetteBob wrote:
Is there a way I can check the other two thru the connector?


Not really.

It could be fuel related, as mentioned, but I'm not looking that direction. You can still do a pressure test while driving to rule out all culprits.
Posted on: 2011/7/19 11:30
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CorvetteBob Re: Hunting Idle, stalling
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Well, I finally made an appt. at the dealership for next Monday. Of course, once they see the SR I'm pretty sure they'll just stop what they're doing and say the SR IS the problem.

I tried calling the only other shop I knew of, but their number is disconnected. I guess he retired.
Posted on: 2011/7/19 13:33
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CorvetteBob Re: Hunting Idle, stalling
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Later today I'm gonna check the fuel pressure. If I remember I need to have it at 42-43lbs. with the Vacuum line off the FPR? Yes or no?

thanks
Posted on: 2011/7/19 16:40
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BillH Re: Hunting Idle, stalling
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CorvetteBob wrote:
Later today I'm gonna check the fuel pressure. If I remember I need to have it at 42-43lbs. with the Vacuum line off the FPR? Yes or no?

thanks


Leave the reg. hooked up, key on - FP at 41-47.

Start the motor, FP should fall 3 -10 psi.

Then remove the vacuum line to the FPR and it should return to 41-47.
Posted on: 2011/7/19 16:53
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CorvetteBob Re: Hunting Idle, stalling
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BillH wrote:

Leave the reg. hooked up, key on - FP at 41-47.

Start the motor, FP should fall 3 -10 psi.

Then remove the vacuum line to the FPR and it should return to 41-47.


Done and it's there.

So far this week I've now been boiled in my own sweat and all I've accomplished is to have cooked the plug wire clamp on my timing light. I'd buy a new one, but Sears parts people don't know what a timing light is, so they hang up on me. The only number on the light is, "Not a Sears number."
Posted on: 2011/7/20 3:41
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BillH Re: Hunting Idle, stalling
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Quote:

CorvetteBob wrote:
Quote:

BillH wrote:

Leave the reg. hooked up, key on - FP at 41-47.

Start the motor, FP should fall 3 -10 psi.

Then remove the vacuum line to the FPR and it should return to 41-47.


Done and it's there.

So far this week I've now been boiled in my own sweat and all I've accomplished is to have cooked the plug wire clamp on my timing light. I'd buy a new one, but Sears parts people don't know what a timing light is, so they hang up on me. The only number on the light is, "Not a Sears number."


I think I have a spare light in the shop that is the spring clamp type (haveta go look). I could peobably get it to you for $10-$15 if you're interested.
I haven't used it in years, bought a better one.
Posted on: 2011/7/20 13:12
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CorvetteBob Re: Hunting Idle, stalling
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I'm interested Bill, do you know what brand it is?
Posted on: 2011/7/20 17:23
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djxib Re: Hunting Idle, stalling
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Bob - in my experience, 'stalling out' in traffic when coming to a stop is either IAC or vacuum leak related - I have had a number of cars (vette and non-vette) where this kind of issue has been fixed by either replacing the IAC or fixing a vacuum leak. MAF cars are much more affected by vacuum leaks (my 92 vette, which is non-MAF, could seemingly care less if I have a vacuum pipe disconnected).

Have you tried spraying your intake with throttle body cleaner? With the engine running, spray around the pipes and seals and see what happens - if there is a leak then the engine RPM will rise. Also try spraying other areas where there are vacuum pipes (although avoid the headers!).

Good luck!
Posted on: 2011/7/20 19:16
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BillH Re: Hunting Idle, stalling
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CorvetteBob wrote:
I'm interested Bill, do you know what brand it is?


Made by Dixson, looks like they are not in business anymore.

This is a plain, vanilla, plastic timing light.

I bought a good one with the adjustable advance knob so, this has been laying in a cabinet in the shop for many years.

The plug connector is the open spring design.
It is what it is.

Attach file:



jpg  2006-05-02 21-00-06_0002.JPG (0.00 KB)


jpg  2006-05-02 20-59-46_0001.JPG (0.00 KB)

Posted on: 2011/7/20 21:28
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Matatk Re: Hunting Idle, stalling
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Make sure you ship that with a return address of Dr. Spock

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Posted on: 2011/7/21 2:49
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Matatk Re: Hunting Idle, stalling
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CorvetteBob wrote:


I've got one of those super duper things you put into your throttle body to smooth out the incoming air. Last year I took the fastener for it out and smoothed it way down in case it was restricting air into the IAC passages. Is it possible that could be restricting air from the IAC and causing some of these problems"?


Bob, I reread this thread, and this point jumped out at me. I recall a problem some guys had with aftermarket throttle bodies and the IAC bleed hole not being there. I seem to remember some air foils covering the stock IAC bleed hole, too, causing problems. GM designed the TB to have a small amount of air coming into the intake past the IAC.

Do you have an aftermarket TB? Does your airfoil cover the IAC hole?

Look at these links for examples:

http://members.cox.net/chipsbyal/page/idle/index.html#stocktbi

http://members.cox.net/chipsbyal/page/idle/tbi.htm
Posted on: 2011/7/21 2:52
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josephf31 Re: Hunting Idle, stalling
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I'd rip the airfoil thing off, I've heard nothing but bad things about them anyway...
Posted on: 2011/7/21 2:54
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CorvetteBob Re: Hunting Idle, stalling
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Quote:

BillH wrote:
Quote:

CorvetteBob wrote:
I'm interested Bill, do you know what brand it is?


Made by Dixson, looks like they are not in business anymore.

This is a plain, vanilla, plastic timing light.

I bought a good one with the adjustable advance knob so, this has been laying in a cabinet in the shop for many years.

The plug connector is the open spring design.
It is what it is.


It sure is as good thing you put that pic up... I've still got a craftsman that has the same hookup. I'm looking to eiother fix the inductive one I have or get another inductive unit locally. Thanks anyway Bill.
Posted on: 2011/7/21 6:00
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CorvetteBob Re: Hunting Idle, stalling
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Matatk wrote:
Quote:

CorvetteBob wrote:


I've got one of those super duper things you put into your throttle body to smooth out the incoming air. Last year I took the fastener for it out and smoothed it way down in case it was restricting air into the IAC passages. Is it possible that could be restricting air from the IAC and causing some of these problems"?


Bob, I reread this thread, and this point jumped out at me. I recall a problem some guys had with aftermarket throttle bodies and the IAC bleed hole not being there. I seem to remember some air foils covering the stock IAC bleed hole, too, causing problems. GM designed the TB to have a small amount of air coming into the intake past the IAC.

Do you have an aftermarket TB? Does your airfoil cover the IAC hole?

Look at these links for examples:

http://members.cox.net/chipsbyal/page/idle/index.html#stocktbi

http://members.cox.net/chipsbyal/page/idle/tbi.htm


Good catch Matt, but I'm still running the OEM throttle body, and I've made certain It not only has the proper gaskets on the Superram, but I made an aluminum plate w/ gaskets on either side to make sure the idle air passages were properly open AND properly sealed as the SuperRam may have caused some issues for uncovered porting on the backside of the throttlebody.


And to josephf31,
I've been thinking of doing just that.
Posted on: 2011/7/21 6:09
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CorvetteBob wrote:

It sure is as good thing you put that pic up... I've still got a craftsman that has the same hookup. I'm looking to eiother fix the inductive one I have or get another inductive unit locally. Thanks anyway Bill.


Didn't know your's was inductive.
It's actually better for me since I don't have to pack it up and go to the post office.
Posted on: 2011/7/21 13:07
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Matatk Re: Hunting Idle, stalling
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I think you should get a good scan and see what the IAC step counts are at when it's stalling or acting up.

Matthew
Posted on: 2011/7/21 21:28
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CorvetteBob Re: Hunting Idle, stalling
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Matatk wrote:
I think you should get a good scan and see what the IAC step counts are at when it's stalling or acting up.

Matthew


That's where I took it Thursday. We'll see what they find. Btw, I took the "air foil" off. When i put the new IAC on, I took a good hard look at the Airfoil. It did have a hole for the IAC to breathe, but I got out my die grinder and opened it up to look like a "Y", instead of the mousehole they had. Also, I ground down the sides of the fastener that goes inside and ground along the back of the airfoil, all to open up any possible restrictions. But even with that done, I still think the drivability was improved a little more by removing it. One more thing, I'm wondering about my a/c compressor. When I put it on last year, it was new and I wasn't able to turn it by hand one bit. I'm wondering if the compressor is still so tight that the engine has difficulty overcoming the drag when the clutch engages. Oh well, it's late. I'll be back to let you guys know what we find out.
Posted on: 2011/7/22 6:48
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Matatk Re: Hunting Idle, stalling
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Looking forward to seeing this resolved....many others have the same issue you describe.
Posted on: 2011/7/22 23:44
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CorvetteBob Re: Hunting Idle, stalling
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Matatk wrote:
Looking forward to seeing this resolved....many others have the same issue you describe.


I got the car back yesterday, but had to go to work. I want to let it start from cold to see if they helped. What they did say is my refrigerant was low causing my compressor to cycle too often. Also my idle was too low. I told him about the minimum idle procedure I did. he said I had it right, but the reality is that setting it at 450rpm is too low. he didn't specify what would be adequate, but 450's too low.
One good thing I got is a written 2-year/24,000 mile warranty on the repair. They don't do that at a dealer!

It sounds to me like there's only so much can be done without altering the programming, so increasing the minimum idle is the regular guy's way to fix the problem. Also, I had a feeling I might be low on refrigerant, but it's been so burned-danged hot lately I'd hafta drive for an hour at night to get the system cool enough to know for sure. I won't be driving it today. Working 7 this week and I'm beat-dead tired. The A/C unit on my side of the bldg is out and we've been running the CNC stuff in 88* temps.(indoor) I'd call in and blow today off, but there's a special place in the unemployment line for those that do that too much, so I just don't do it at all.

I'll try to get some seat time in and let you guys know how it's doing.
Posted on: 2011/7/23 18:03
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CorvetteBob Re: Hunting Idle, stalling
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I finally got to drive it to work today. It ran great! When I started and backed out it didn't even think of stalling much less a single sputter. I drove thru the area where it always dies, this time it ran great! So the outcome is ..............(drum roll)
So far, so good.
Posted on: 2011/7/28 2:02
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TommyT-Bone Re: Hunting Idle, stalling
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Sounds good.
Posted on: 2011/7/28 2:21
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Matatk Re: Hunting Idle, stalling
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Glad to hear that!
Posted on: 2011/7/28 2:26
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