Hey forum,

i've been having this odd problem with the stang recently. when i cold start the car, it starts up fine, but after i drive for 10 minutes and the car gets warm, if i turn it off and on again it will crank and start no problem but the idle will surge up and down (900-500rpm) and almost stall for a few seconds then it will smooth out.

what could this be? its driving me nuts. thanks.

 

I'm wondering if it's a vaccum leak, or have you checked the battery cables for any loose connections?

 

There are a few things that come to mind for me. First thing I would check is for vacuum leaks, its the easiest and most cost efficient solution lol. Use a can of WD-40 and spray around the upper/lower intake seams and vacuum lines. If your idle changes then you know you have a vacuum leak. Take note of where you were spraying when the idle changed to pinpoint the leak.

Second is the IAC. Lots of people pull these out and clean them, which is usually not very effective. If your IAC is bad your engine will constantly hunt for idle.

Lastly, the MAF is one of the most common problems I encounter on customers cars that stall, idle really bad and lack power. (my 5.0 included!) Using the wrong sampler tube on the MAF for your injectors will make it want to die too

 

thanks guys, i will start checking for leaks. its an 88 so its a speed density car and doesn't have a MAF. It has a newer IAC and i took it out and cleaned it anyway.

any specific hoses i should be checking for leaks? there are so many....

also something else i noticed was that when im driving in lets says 2nd and go into 3rd, when i press in the clutch its like the rpms are staying up a bit, like im pressing the gas pedal and clutch while shifting. this is why i was leaning towards some sort of a leak.....

 

If it is a leak it could be anywhere, time is not kind to any gasket or rubber hose! Any vacuum line you see is fair game.
The hanging idle during gear changes is typically IAC or TPS related. Before you throw any parts at it check and make sure the TB is clean and closing properly when warm. Ensure your TPS is set correctly. If it is, I would start at the IAC.
I know this may seem stupid, but is your ACT plugged in and in good condition?

 

whats an ACT? where is it located?

 

Sorry for the late reply, but the ACT stands for Air Charge Temperature Sensor. I found a picture on google that points right to it cause hey pictures are easier to understand. What the ACT does is measure the temperature of the incoming air which helps adjust your fuel/air ratio.
Have you tried anything suggested yet?

 

I have the same issue on the 87 GT I'm thinking IAC as it is the original one along with the TPS. FastEd has a few so I may swap the IAC just to see if it changes it. Probably do it tomorrow will LYK if it fixes it.

 

Swapped the IAC no change.