Engine RPM's stay up

91BLOWNSC

Registered User
Just got my engine back together have having it entirely rebuilt. Definitely a huge process, and just started it up tonight. Runs pretty decent except when you blip the throttle a bit the RPM's want to stay exactly where you rev'd it too. I think I have all the vacuum lines in the right place. Any idea's what might be causing this? And if it is potentially still a vacuum line, any ideas of the specific ones I might look at?


Thanks!
Mark
 
The IAC is not new, was the one that I previously had on it. If I don't rev the RPM's will stay low and for the most part will idle correctly. For the 10 minutes I had it idling it did sputter on more than one occasion where it almost wanted to stall, then would go back to normal and idle fine. I am not even sure where to look at this point.
 
How long was the engine down?

Vacuum leaks are highly suspect in your example, so be sure to get all lines connected and snug, also the intercooler joints.

If you can make it idle high again, disconnect the wiring harness at the IAC and see if that has an effect. Wack it with a soft mallet, etc. during a high idle to see if it's hung up...

Also confirm the throttle linkage isn't hanging up/binding, maybe being held open by a floor mat.

I had a mystery high/hanging idle just last week that a new IAC cleared right up, but I'm not dealing with an engine o'haul, so....you can have any combination of things you may need to check over before you find the culprit(s).
 
Last edited:
I would def look at iac especialy if u went with bigger t/b I changed t/b had same thing goin on changed my iac with the new one I had already had just trying to be cheap and get the most out of the old one and as far as wanting to die could be iac vaccum leak or maf sensor bad
 
Any mods done along with the rebuild?

Vacuum leak is my guess without additional information. IC tubes are the usual suspects.
 
My car did this as well. I had no mods. On start up it would idle ok sometimes and other times not. It would hang at around 1800rpm or 1700, sometimes 2100.
Everyone said a vacuum leak, I smoked it 2-3 times with nothing.
Everyone kept insisting that it was a vacuum leak because I could unplug the iac, and it would still run.

I finally just bought a new IAC and it solved the problem. The plastic accordion in the old IAC had cracked and broke AND it wasn't even working.
 
Ive had problems recently even with a new IAC. With the A/C on (which instructs the EEC to raise the idle) it will rev and stay at 1500. Which sucks because you have to push the brake harder to hold it up.. :mad: Until I can figure out whether or not the problem is the IAC or the EEC or something else, what I have to do is slip it into neutral and floor the pedal to get it to find the right idle. Then things are OK until it does it again. I haven't noticed the problem with the A/C off, but that could be a coincidence.
 
Most likely you have a vacuum leak that is causing the IAC to have no control to get your non a/c idle. Then when it tries to deal with the A/C it will overshoot. I suggest checking for a vacuum leak somewhere. Either the Intercooler tubes leaking, or the plenum attached to the intake manifold, or any of the number of vac lines connected to the motor.
 
Back
Top