Buisson 91TPIZ28&91B4C

My car idles warm at 1100 to 1250...It's don it since the rebuild. Ive replaced the egr system, IAC valve, TPS, replaced plenium gaskets, rebuilt the TB and so much more.. When I go through the set idle procedure I can get her to stay at about 550 or 600 rpm with no prob. As soon as I rev the motor or start it a few times its back up there. Im getting no comp codes. I'm questioning the MAP sensor.
HeLp PlEaSe!!!!!!
91 B4C freash rebuild on the whole damn car with a coulple extras.

kevinc

Sounds like you have a vacuum leak.

Easy to diagnose if you have access to a scan tool, with the engine running check the "Desired idle RPM" and "IAC Counts" data. A vac leak will show a normal Desired Idle RPM which is much lower than what it's actually idling at, and the IAC will be pegged at zero (0) as the ECM tries in vain to bring the idle down.

If you don't have a scanner or a laptop with Moates software and an ALDL cable, consider getting one. Makes troubleshooting much easier as you can see what each sensor is reporting and what commands the ECM is sending. Search the boards for 'Moates' and you'll find info.

Lacking a scanner, you can probe for vacuum leaks the hard (and dangerous) way using flammable aerosol stuff. I don't recommend it.

TransamGTA350

iTrader: (2)

Start with the simple things. Have you checked the throttle cable for binding? That would be the first place I would look. A vacuum leak is possible too like it was stated earlier. Make sure all the vacuum lines are connected and in the right places. Other than that, probably an intake manifold leak.

72LT1VETTE

You can buy canned smoke to check for vacuum leaks or use the cheat method. Plug the PCV hose, remove the air filter and being careful of the fan/fans, place a piece of cardboard in front of the throttle body. If the engine dies, check the operation of the IAC. Loose connection, not tightened securely or even a dirty seating surface, allowing excessive air flow. Other possibillity, low engine vacuum causing the MAP sensor to respond erratically.

Zepher

iTrader: (1)

I have a similiar problem on my 86 Trans Am.
I installed a TPI setup, Crane PowerMax 2050, 52mm TB, headers, and exhaust.
Mine idles at 1100 when warm, pulls 15lbs of vacuum.

I can't get any data out of the computer, I think the Serial Data Link isn't working on the ECM.

Der91Z

iTrader: (1)

I would look at the TPS and see if that is set right. I had a similar problem but when I adjusted the TPS, it fixed the problem