philly3384

ill go shoot myself in the ****en back yard if this doesnt get fixed soon. The car idles up and down on a cold start then idles fine... then i rev the car and the idle hangs there and when i shift from gear to gear the rpm's stick for a sec then finally drop.

settled4automatic

ha! that's exactly my problem lol. let me know when ya figure this one out!! i've always been told vacuum leaks :P everything else that people said to check was fine on my 87 gt. i haven't taken my upper intake off to get to the rest of the vacuum lines tho, so i'm hoping there's a leak there so i can think i figured it out

Djs94stang

Put a vacuum gauge on it and check the vacuum. There is one vacuum line that is impossible to get to unless you take the upper intake off. I took my upper off to change fuel injectors and the vacuum line on the underside of the upper intake was just about ready to fall apart. I don't think I could have gotten to it without the upper being off the engine.

Check that the IAC is working correctly. This usually controls the idle and could be getting stuck.

roundman

pull and clean the throttle body and the IAC with some good carb cleaner and make sure the throttle plate is completely closed at idle so that the IAC can do its job of controlling the idle speed. there is always some carbon build-up on the back side of the throttle plate due to the EGR system and this can prevent the throttle from closing completely and lead to a rough idle.

88GT40

could be what my prblem was i fixed all my vacuum leaks and the problem got worse t turns out my lower intake manifold was the major leak, and i had to replace that gasket.

mustang8719

I was there about 2 months ago.

yakini

I had a similar problem for a long time and tried everything that was said here. IAC, Tps, vacuum lines. In the end I found out it was the lower intake gasket at the back of the engine. Found it cuz it was leaking oil (only on the highway of course which had me lost as to why I was losing oil only on the road). Never saw puddles in the driveway and since it was leaking in the back it looked like the rear main was where the leak was. Fortunatly my mechanic knows his sh@# and found the leak. Turns out it was leaking good enough to let air in occasionaly which had my computer making the idle hang up and act confused. It also had the engine temp and gas mileage all messed up. Got it fixed and it idles like a new car and runs at a steady temp now. I have seen a million posts on here about idle surging and the IAC fix seems to be the most common suggestion and doesn't seem to fix half of them. Try this.