hello. my 99 gt isn't idling correctly. its all over the place. after its been running a bit, the needle dips down to below 500 rpms. carmax said they can't find anything wrong with it. any ideas?

 

Could be a lot of things, but seems like you have the dreaded "hunting" idle. What mods are done to the car? You could have an after market throttle-body that is not set right or a CAI that is messing things up.

Tell me more....

 

could it? also be the IAC if its a stock car??

 

iac [idle air controll] thats probly what it is

 

IAC is a likely candidate.

 

Wouldnt assume anything until we know whats done to the car.

 

The car is completely stock. carmax fixed the idle control when i first got the car. that was the first thing they checked when i brought it in the other day. said they couldnt find anything wrong

 

chances are it is an IAC problem and most IAC problems can be from not changing the PCV valve at the normal 30k intervals, or the use of and "aftermarket" IAC or both.......how many miles on the car?

 

it has around 78k. do you think changing the pcv valve would fix it or should i go ahead and get another shop to inspect the idle control

 

I have the same problem with my car. Its so bad it will even die on me when its trying to idle. I have 100K miles and a BBK CAI. The intake was on the car when I got it and it's always had that problem. Would replacing the PCV valve probably fix this problem? And how much would that cost? I've never priced those.

 

Id replace both the IAC (@$70.00) and the PCV valve (@$6.00 to $12.00)....PCV valves should be changed every 30k under "normal" driving conditions, also inspect the rubber hose going from the PCV valve to the plenum for cracks or holes......

 

I had the same problem with my old 2000 GT. I had no mods with about 75,000 miles... turned out to be the IAC. It would drop RPMs and die a lot. I put a new IAC in and everything was fine.

 

+1 i had a 01 and the iac went out and the damn thing wouldnt stay started unless you held it about 3000 rpm.

i'd take it somewhere else. hell around here the ford dealerships and the "discount" guys are almost the same damn price.

 

Could just be an air leak after the MAS.

 

i agree with stromsgt, i just had this problem, and it was a leak in my intake.