Bear with me hear, i am from the Hi Perf environment of BBC an SBC Carbs and No Computer stuff.

I have ended up with a 89 C4 Vette that i can't understand what is happening.

The car needed injectors "they were leaking pretty bad" so i replaced them with a set of New Bosch III 22LB. Prior to the injector swap the car idled smooth and responsive except when it warmed up then the idle got a bit rough but still ran well but really sounded like crap at idle, and was hard to start untill the fuel had evaporated from the cylinders or had set overnight.

So i replaced the injectors,rotor bug,cap,plat plugs.045, when i first started the car after the above changes i had cleared any codes and let it idle for about 10-15 minutes for the computer to relearn. It was idling at around 1200 and never would come back down, so i adjusted the torx throttle adjustment down to 800 then drove the car about 2 miles it doesn't like to idle and sounds like a junk heap at an idle but runs well with no complaints above 1500. I have ran codes and came up with the 15,22,32 what i don't understand is how these codes can make the car sound so sick and barely idle, but yet run fine at cruise or WOT.

Can someone please explain to me what is going on and how the TPS,IAC,Coolant Sensor can have this much effect on sounding and acting so sickly at idle?????

I am just trying to understand and the shop manuals don't explain anything...

Thanking you in advance and sorry for the rant!!!!

make sure the tps is adjusted correctly. check your fsm for voltage adjustment. dont quote me but i think its a 050 volts. you will need a scanner to set this.
next remove the iac and clean the tip of it. then clean the port in which it is mounted with some carb cleaner. make sure the port is clean and open.
next i would replace the coolant senor located in the left cylinder head. their cheap $15.00?
now fire it up and let it warm up. at normal operating temp. the tps should a voltage of .50. check your fsm for correct voltage required and this is at normal idle conditions. if not adjust it. also you can take ohm readings on these parts. with key off of course. unplug each one and take your readings if not in specs replace it.

Codes are as follows:

15 = Cooler Sensor Circuit (Low)
22 = Throttle Position Sensor (Low)
32 = Exhaust Gas Recirculation Circuit

Did you have any codes before or were these codes all generated after?

Sources of poor idle can be a vacuum leak. If it was running poorly before, a bad coolant temp sensor (CTS) can cause that. The TPS should be adjusted according to the FSM. When you reconnected everything, did you reconnect the EGR valve, etc? Are all lines hooked up? Did any break? I broke a couple of old vacuum lines doing mine since they are brittle.

The FSM will have a diagnostic chart for each of the codes shown above. By following the chart you will be able to determine what parts are good/bad.

Matthew

Welcome to Corvette Guru!

Thanks for the reply,The EGR Valve was locked open and i removed a chunk of carbon and freed it up then checked its abilty to hold vacume and its fine now and smooth and free, but still have the EGR Code?

As far as the IAC no code but i did clean out the plenum real good before reassembly with carb cleaner with the IAC and TPS still installed should i remove both of them and clean?

how does a coolant temp sensor affect idle quality? just trying to understand.

Welcome aboard. Do you have a factory service manual? Quote: That screw is not to set the idle. It is to set the base idle which is different than the idle you wanted to adjust. If you did this to set the idle then you need to readjust the low idle as per the manual. Is the car an auto or stick? TPS voltage is .54vdc.

I'm doing this from memory as I had to readjust my idle recently. To set the base idle you need to put the car in neutral if stick. disconnect the AIC and then set the idle with the idle screw you adjusted earlier to I believe 450rpm. Then you set the tps voltage to .54v. Then you hook up AIC and let the car idle for a few minutes so the computer can reset it for cor correct position. Shut the car off and start to check that idle is about 750 rpm.

Now this is from memory as my manual is in Portland with my wife and car and I'm in Indiana and is for an 85 so the 89 may be slightly different. I don't remember the differences for the auto but I think you put the car in neutral also or drive I don't recall. Some one with a FSM will look it up and correct me.

Hope this helps. Again welcome aboard these guys are very good and we're all here to help.

Mike

Thanks, i guess i will start there and give that a shot, I guess i am going to have to learn patience with this electronic stuff..........

Quote:

There is no code for faultly IAC operation

Coolant Temp sensor(CTS ) ; at intake front is the biggy in terms of engine operation.
The ECM is programmed to do different functions and nearly all of them have a temp related setting.
If the ECM is not seeing the correct actual engine temp then it will not be applying the correct outputs.

Say the engine is at operating temp and the CTS is reading low temp then the ECM will be still supplying extra fuel ( like the choke on your BBC ) assuming the engine is not up to temp.

Do not be confused about what the temp gauge is reading.This has it's own independent sensor( pass side head, rear) and is not indicative of the reading the ECM is seeing.
Like Captmike states above; you will have to reset the "idle" screw back and read adjust TPS /IAC

Full details here

http://www.corvetteactioncenter.com/k ... rly+C4+TPS+and+Idle+Speed

Quote:

Sensor locations.87 -89
One wire units ;
LH front is fan switch for 2nd fan if fitted
RH rear is gauge sensor.
Two wire sensor at front of intake is the CTS

Glad to see I was close by memory. I forgot about the paper clip. Sorry about that.

Quote:

You do these things 100 times then you forget something and have a WTF moment; I'm sure this worked last time

Quote:

There is no code for faultly IAC operation

Coolant Temp sensor(CTS ) ; at intake front is the biggy in terms of engine operation.
The ECM is programmed to do different functions and nearly all of them have a temp related setting.
If the ECM is not seeing the correct actual engine temp then it will not be applying the correct outputs.

Say the engine is at operating temp and the CTS is reading low temp then the ECM will be still supplying extra fuel ( like the choke on your BBC ) assuming the engine is not up to temp.

Do not be confused about what the temp gauge is reading.This has it's own independent sensor( pass side head, rear) and is not indicative of the reading the ECM is seeing.
Like Captmike states above; you will have to reset the "idle" screw back and read adjust TPS /IAC

Full details here

http://www.corvetteactioncenter.com/k ... rly+C4+TPS+and+Idle+Speed

Quote:

Thanks for the explanation, i was not aware the ECM used a seperate sending unit for temperature. I guess i have alot of troubleshooting to do this weekend! I will be diving right into the world of auto computers this SUKS!

Quote:

Not hard , if you found your way around carbs and dist OK then you have the same functions with EFI , only electronically controlled.Where you used to set your spark advance with weights and springs the ECM does it from a program

Lots of good info out there for EFI dummies.
simple one on L98 start up
http://www.corvettebuyers.com/c4vettes/l98.htm

Good News worked on the Elimination of SES 15/32/22 Codes this weekend and all are gone!

I reset the TPI Idle by the book also reset the IAC and Tested the CTS per Manual and it failed so i replaced the CTS as well. Cleared computer of codes and started Vette and let it idle etc for about 15 minutes all seemed well and all codes are now gone.

So i took it for a casual 10 minute drive all seemed well. Then i lit it up a few times on the way home and it ran like a scalded A$$ Ape upon pulling into my neighborhood it seemed to be running rough so i let it set in the drive way and idle for a few minutes and it was still running pretty rough, so i turned it off and checked for codes still no codes all are still gone just flashes a 12. SES Light is only lit when key is turned on and then goes out immediately when started.

So i start vette back up again its still running rough i let it idle for about 10 minutes and it finally cleared up and smoothed out to where it was fine again, drove it a mile or so down the road and was fine, but if i kicked it in the A$$ a few times it would run through all the gears strong but when i would bring back down to normal cruise it would start running rough again and would smooth out after about a 10 minute idle?

Also the fuel reg/ dizzy cap /rotor bug/plat plugs and bosch III's are brand new.

Does this seem like a Fuel flow from tank or a Heat soak distributor module problem, any ideas appreciated!!

Ever replace the fuel filter? Could still be a fuel issue with the pump/sock or junk in the tank.

If it's a heat soak issue (aka ICM) it would usually die and not restart.

Glad you got your other issues worked out so far.

Matthew

Also, when's the last time you checked your timing?

Thats kind of what i was thinking,junk in lines or tank. I haven't checked timing recently cause i didn't really think it could cause that besides Vette pulls hard from 1200 on up thru the RPM's.........

Timing can affect idle and acceleration in a negative manner. Once you're at WOT you won't notice it as much because the computer is adding so much timing to it.

Replace the fuel filter just because it's a maintenance issue. Ever replace your o2 sensor? Not your problem, but another maintenance issue people just forget about.

Matthew

I will check the timing and yes the O2 has been replaced. What is base timing?
Where is the fuel filter on the 1989 C4?

Timing/emissions label is on the d/s of the radiator shroud, 6* btdc. Fuel filter is under the car along the frame rails near the front jacking area on the passenger's side. Just look under the front door/hood seam and you'll see it.

Matthew

Thanks for the info.........

Dry, I'm glad you got this car.....it was prolly a nightmare for the Previous Owner.....you seem like the type that understands the fundamentals.

You know where you want to go......you just need to know which road is the best way to get there.

You have issues after romping it....what temps are you seeing after you shut it down and allow it to idle.

Yeah, i know its just a matter of getting the kinks worked out that nobody really ever wanted to straighten out.

The Vette actually is running very good now except for after romping on it a few times for an extended period of say up thru all the gears manually to 100 or so, with in about 5-minutes of doing this is when stopping at lights or entering neighborhood low rpms it sounds ill again and idles very rough (will rock car side to side) but if left idling in park for about 10 minutes all is well again.Can an IAC cause any idling issues like this? The IAC seems to be working properly just wondering, because when i cleaned the plenum off the car with throttle body cleaner which was super filthy inside i didn't remove the IAC.........As far as temps it runs up to 232 fan kicks on it cools down to 220 and repeats just sitting in park idling after bringing it back home from a test drive.

I would clean the port for the IAC and take the IAC off and clean three also. That can get really dirty and cause some problems.

Thanks again........
I guess cleaning the IAC Port and IAC Unit and changing the inline fuel filter is next on the agenda. Is there anything that can collapse filter wise in the tank/pump?

232°???.....It's heat related. Something is not right with those temps...then it sits and idles and cools down and starts running right again.

232 is about when the auxillary fan comes on. Main fan should come on at 228 or 229. I don't have my FSM in front of me. I would venture to say that the area between the condenser and radiator is clogged with a whole bunch of leaves and crap. Take the radiator shroud off (there are a ton of screws) and blow out all the crud with a garden hose. That should bring your temps down a bit. Don't be overalarmed by those temps, GM "designed" it to run at higher temps for emissions and longevity. You'll hear guys talk about how important it is to run a 180* thermostat, but it's bs. If you're concerned about it you can add a switch to turn the fan on at a lower temp.

Matthew

Quote:
You may be right.....I've not seen evidence either way from GM....but in my day to day work.....I'm involved in a ton of design....never never never have I heard "Heat will make it 'last".......more to the contrary.

We are always trying to remove heat for longevity