[fastford3388]

I had a similar problem with my 89 GT. It ended up being the EGR Position sensor and the TPS sensor that went bad. Is the check engine light on?

[NoPHONYpony]

U should check the EGR valve it might give u a shitty idle at low rpms and idle it will prob also be running lean

[93GT]

for any vaccum leaks what i would do is take a can of brake clean and start your car when its cold and spray where you think there is a leak( all of the lines around your upper plentum) you will here the motor run better if you have a leak in that spot.

[Overkill]

Assuming your tune-up is good (if not you need do that first anyway), and you've checked the IAC and TPS (both are easy and part of a decent tune-up) I betcha it's a vacuum leak. There are only about a thousand places for a leak, the most likely have been posted already, but the hardest ones to get to are probably where the problem is, mainly under the plenum, like jsj_297 says.

I once had a vacuum leak that drove me nuts. I eventually tested every single line, connection and component. I found and fixed mostly a bunch of cracked and gashed lines and a leaky smog pump valve, but got no appreciable improvement. Turned out the little ball shaped vacuum reservoir inside the passenger side fender had a crack in it. Got one out of a junker, hooked it up and the problem was over.

[lugnutz08]

Its probably been siad but check the ground from the drivers side head,theys also a green ground between injector #3-4,prolly not the problem but alot of people forget the small stuff

[haywood11]

check the tps and make sure its adjusted properly.