Chasing old idle issue -95 5.0 L, 5 speed

[Richard P]

Been chasing this issue for several years off and on but it still alludes me. Car has 78 k miles and runs ok above idle. The check engine light has never been on and last time checked, no codes showed up. When started cold it will idle down fairly quickly but then the idle starts to vary from about 700 to 900 but regularly drops to almost stall condition. When accelerating from a stop, rpm will briefly increase about 200 rpm between shifts. In general, it just seems to have a 'weak' idle and will easily stall from a stop when the clutch is disengaging.
I've attached a short video clip of engine idle operation that I took this pm. Sorry for poor quality of the video but it kind of demonstrates engine operation at idle.
Any thoughts on what the issue as I'm tired of spending money for new sensors and the like that don't change anything?
Thanks for any and all advice.
Richard

 

[da8banger]

Hey man, read your post. what sensors did u replace so far?

Im the 2nd owner of a 95 GT. the 1st owner gave me all the maintenance papers, and around 90-100k he described a problem similar to yours but worse. the car would shut off by itself at a stop/idle consistently.

He ended up taking it to the dealer and they replaced the IAC solenoid. That fixed the problem and to this day never had issues with the car stalling by itself.

When i got the car i did notice the idle was rough (liked to idle and shake the car up at around 400 rpms) so i ended up doing two other things:
1. I adjusted the IAC (theres some videos on youtube and I think LMR has a written guide on it) to increase the idle speed. I adjusted it to around 900-1k RPMs.
2. I replaced the 2 oxygen sensors near the cats. That helped a lot to keep my idle stable with the AC on or off.

I would suggest trying to adjust your IAC and resetting the idle since thats free. Then maybe try the oxygen sensors or IAC solenoid next

 

[RAU03MACH]

there is a adjustment screw on the right side top has a cover that is on throttle body
adjust in or out to keep a good idle keeping it from dying when stopping or turning the wheel \
just make sure you count how many turns in case you need to get it back in specs

on mine i have it just about all the way out to keep it running
good luck on that

 

[Daryl]

Rau03Mach walked me thru this same issue. I’m also idling at 950rpm. That and the IAC restrictor plate/gasket (solved the hanging idle issue) and all is well

 

[ttocs]

what has all been done to the car? The only time I have had idle problems was when I was running a pro products brand throttle body. When I switched brands it went away.

 

[Mustang5L5]

I'd check for vacuum leaks. Smoke test if needed.

If you unplug the IAC, where does it idle at? Does it stall out? Often times symptoms like this can be caused by the idle stop screw not being opened enough and the IAC is the sole source of air for the engine in maintaining an idle. Ideally, with the IAC unplugged the engine should barely idle on it's own. The IAC just adds a small portion of airflow to maintain idle quality and account for load on the engine, like AC usage. Often times if the IAC is the sole source, you get easy stalling and erratic idle due to sluggish movement of the IAC.

I adjust the idle stop screw with the IAC unplugged to a very low, but stable idle. Then i plug the IAC back in, unplug the batt for a bit to reset the ECU learned parameters and restart and let it relearn idle over a few start/stop cycles.