My 91 idles at 3000 rpm when I start it. I have replaced the TPS, IAC and ECM, but can not bring down the idle. Any ideas?

Throttle plate is not closing all the way ?

Reset ECU, may run a little weird at first, there is a learning curve, which should last about 150 miles. My idle sucks till the car warms up too.


-justin

Clean the Throttle Body.

Its a 91 SE 3800 V6. I ran a scan tool and got a list of codes. 21 TPS Signal volt high
24 VSS short circuit 25 MAT sensor signal high 27 2nd gear switch 29 4th gear switch
39 TCC problem 66 ECM reset

Yes, everthing is plugged in and I live in southea

Sorry, southeast WI Any help would be nice

I got the ECM new from advance auto parts. I had taken the car to a repair shop to have the system analized, they told me it was a ECM problem. Yes I did swap out the Mem-Cal when I replaced the ECM.

Any ideas for troubleshooting the idle problem?

A guy at work mentioned an IAC motor, any ideas?

If the PCM is working fine and its not a ghost code then its possible the TPS could still be a problem. I played with mine and got it to idle at ~2k without much adjustment. You gotta remember, its the only way the computer knows if you're pressing the gas in park, for all it knows you have your foot on the acclerator when you start it. If you have a voltmeter you can test it real quick. Punch the very tip of a needle into the TPS wire closest to the TB opening. If I remember correctly with the key on engine off you should read ~5v there. IIRC it should read ~.3 on the next wire over.

Can you keep it in overdrive?
Does it downshift with relatively little movement of the gas pedal?

With foor off gas and key on the middle wire of the TPS should read .38-.42 v (less than a half volt) to ground. At wide open throttle it should read in excess of 4.2 volts.

My experience with very high idle (over 2k rpm) has been more likely a throttle plate that does not close all of the way (mechanical problem, not electrical). For that matter a gummed up IAC (can also cause but usually limited to about 1200-1500 rpm) can contribute and if both are sticky...

I will test with a voltmeter, how do I adjust the TPS.