LittleNo

i have here a 91 V6 3.1L which idles at around 2000, it has no codes and drives fine (ok, you always have to stay on the brake because it accelerates all the time)

here's what i did:
- did the IAC-learn procedure
- replaced ECM
- replaced IAC
- replaced Pickup Coil and EST module
- checked for vacuum leaks, found none but replaced intake manifold gasket

now i searched here on the forums for similar problems and found many threads about 91 3.1's with the same issue, but no one came up with a solution.

Since this seems to be a typical problem on that car, does anybody now what causes this?

91SpeedCam

I was probably one of those threads that you saw. I never got around to posting the fix for the car and I should, but here is what worked for me. I have no clue as to why it worked but it did. I replaced the ignition coil. I did the whole runaround similar to you, even so far as changing computers(had a spare at the time) but change out the ignition coil and see how that works out.

another thing, does the car feel like it has no power, cause mine was pulling 15 degrees for some reason when the issue arose.

LittleNo

i have a spare ignition coil, so i can try this, but when driving it has a lot of power (sure, as lot this V6 can have )

n8_camaro_92

after you replace tha aic ou have to manually turn the idle down theres a setscrew on the back of the throttle body

91SpeedCam

No, don't mess with that screw. That screw that n8_camaro_92 is talking about is used to set the minimum air. The computer will compensate for any messing with this screw that you do. This is why in the guide on this site to adjusting the minimum air, the IAC must be disconnected.

Also just for info, after installing the IAC you don't have to adjust anything, hence the beauty of computer control. All you do is cylce the key, becuase the ECM will drive the IAC pintle out until it stops, and set this as the park position.

From the Park position the ECM draws the pintle out to approximately 160 counts, give or take 3, in order to get the engine running. So its strictly plug and play. Just make sure that there aren't any codes after the IAC installation.

But with my 3.1 I had to go to about 3/4 throttle to keep up with traffic off of the line, so yeah it was lacking a lot of oomph when the problem arose.

-Scott

Al Hasse

Might be the coolant temp sender. Mine started to go out and did the same thing, idled about 2000 when warm, but threw no codes.

LittleNo

so i did it

oh sorry, i totally forgot that one (it's been two month now i'm trying to find out whats going on with that car): that was the beginning of the whole issue: the CTS did not show a code but the temp (read with a Tech2) often showed around -11C while the coolant was at operating temp, so i replaced the CTS with no change on that - the next step was to check the wiring, i couldn't find any real damage but some areas in the harness where the outer isolation was broken, so i put in a new sensor wire from the sensor to the ECM - that also brought no change, so i replaced the ECM and with the new one the temp-issue was gone.

In the past 2 month there where days the car ran absolutely fine, perfect idle, perfect throttle response ... since yesterday the high idle is back

nd4spd42085

this is pulling at straws

but have you checked to make sure the throttle cable, or throttle valve aren't binding? maybe your throttle body simply isn't closing all the way... seems stupid... probably a bad idea... nevermind

one quick question though...

how much does a car like yours cost in decent shape in Europe?

LittleNo

yep, i tried, i disconnected all throttle cables and closed the throttle by hand pressure, so there everything fine

well, in really good shape they are worth good money, let's say 5000 Euros for a Third Gen, and may be 10K Euros for a 4th Gen, all with V8, but that means they must be really perfect. Most of those cars are in really bad condition because most of their owners only drive them, they don't spend any money for fixing issues. A car like this one here (it's a buddies car) is nearly worthless, because you would have to spend a lot of money in a shop to get everything fixed, and the road taxes for older cars are rising from year to year, so for this one it's 400 Euros per year right now, and may be next year it will be 800 Euros.

Firebat

iTrader: (7)

My 3.1 idles at 3000, especially when its cold, then drive it around and idle goes down around 1000. I would be happy with 2000 at cold/startup.

LittleNo

i understand you, so many are having trouble with those 3.1s, i can't believe no one has figured out what causes this ****

Maverick H1L

iTrader: (8)

Does it idle down at all? I've been hearing a lot about this stuff lately. You said you replaced the IAC, so it can't possibly be dirty yet, and we can rule that out. The next thing you can check is to see if the ECM can command the little bugger to close. You can either pop it out of the TB, point the pintle end into a rag, and cycle the ignition on for about ten seconds and back off again, at which point the IAC pintle should extend out of the IAC if everything in between the IAC and the ECM is good. Or, you could disconnect it and the ECM, and run a resistance test on each wire in the system.

Another possibility is a vacuum leak. Sometimes a vac leak just lets more air into the engine and increases the idle a little instead of killing it.