My idle jumps between 600 to 1100 rpm!? I have changed the IAC, cleaned the TB, I made a the "mini air set procedure". The "funny" thing is that with the engine warm and the IAC disconected it idles fine at about 600rpm.
What vaccume "devices" are used to controll idel, how is it hoocked up?

 

Check the manifold vacuum and exhaust for leaks.

 

How do I check the vaccume? Where do I hook up the "vaccume" gague? And could it be a bad TPS? I did get a SES light for about 2 sec when I whas in stop and go traffic. It whas code 22 TPS.

Regards

 

Your ECM controls your idle speed. Your ECM has a table of coolant temp and target idle speeds. Depending on your engine temps it will have a target speed it will try to reach by opening/closing the little airway with the IAC. So to answer your question your computer uses your coolant temp, target idle speed, and RPM to control your idle (using IAC).

My 1994 Vette has a targe of 750 RPM once the engine is warm. It is set around 900 RPMs or so when it is cold for start up.

There is also some functions that control it during coast down. Once you take off down the road at part throttle it will open the IAC to a set position so if you were to jump off of the throttle the motor won't die or drag down so bad.

When your A/C compressor kicks on or off the computer will have to make adjustsments to bring your idle back to target but I don't think this is your case.

A jumpy idle could be exhaust leaks (o2 sensor picking up false reading), maybe your TPS is reading high so your computer is going out of idle mode.

Vacuum leaks can make the idle jump. Your engine gets extra air and the idle goes up, your computer sees this and closes down the IAC control and the idle goes back down.. this keeps going and going.. and going...

I never could get my 406 TPI motor to idle worth a crap... it idled like a blower car.




[Modified by Red94Vette, 8:51 AM 5/29/2002]


[Modified by Red94Vette, 8:52 AM 5/29/2002]

 

well i found out what it is.. My TPS is reading 1.3 volts at idle. I "forced" the TPS to .056v and it idles perfect. What could cause this? Bad TPS or bad ECM?
I strange thing is that it reads ok at WOT, about 4.7 volts..

Regards

 

tt

 

I have no idea what would cause your TPS to get that far out of spec, but it sounds like you have it taken care of now. :cheers:

 

:eek:

 

Can you set it to be at .54-.58 at idle? Mine went crazy from washing the engine. it was at 2-4 volts at idle, even when I pulled it off the throttle body. just replaced mine.