90tararebird

iTrader: (4)

idle way to high 1300 rpm in park 1000 in drive.put in new iac and set to specs described here. then it goes back to high idle when finished. any suggestions

Nixon1

Vacuum leak? Has the idle stop screw been tampered with? TPS adjustment is another possibility

90tararebird

iTrader: (4)

i thought that on my 1990 that tps is not adjustable. is this a part that will go bad? does not appear to be any vac. leaks. the stop screw has been touched. i do not think this is the problem since i set the iac correctly.first time i start it after setting iac idle is fine after that it jumps.

Vader

"Set to specs as described?"

What specifications? The IAC is not really adjustable. What you need to adjust is the throttle plate minimum air position. With a fully warmed engine, the IAC needs to be parked fully closed, then disconnected. Restart the hot engine, and set the idle RPM to the specification. On an automatic, that's usually 550 RPM in DRIVE. The actual spec is on the VECI label on the underside of your hood. Once it is set, shut off the engine and reconnect the IAC.

Important things to note:

1. Use a separate tachometer to set the minimum air position. The factory in-dash tachs are woefully inaccurate, and may be part of the percieved high RPM problem.
2. Clean the throttle body and IAC passages thoroughly before any adjustments.
3. Make sure the throttle cables are moving freely and not binding before adjusting anything.
4. Make sure the PCV valve is clean and operating correctly.
5. Check the TPS voltage with the throttle in the idle position. You should read no more than 1.0VDC

90tararebird

iTrader: (4)

i did not word that correctly i adjusted the idle using the instructions in the tech section. i did not adjust the iac i adjusted the idle.throddle body is clean.pvc valve is new.i will check the throttle cables and the tps voltage.

Nixon1

Just to chime in--does not *appear* to be any vacuum leaks---appear isn't good enough. Trust me! My friend's 90 Firebird, we found a TINY vacuum leak on the cluster above his throttle. It was caused by one of the old lines that didnt fit on quite right. So we fixed it and it made one HELL of a difference. These motors are so vacuum sensitive it's ridiculous...so go over ALL of the lines. If you suspect you might have a leak somewhere, or just want to double-check.... Get a can of THROTTLEBODY CLEANER, and mist it around the engine bay near various vacuum points. If there is a vacuum leak and you get the spray near it, it'll be pulled into the engine and it will rev up a little bit when it burns it.