Rough, loping idle and random attempts to die


New Member
Apr 18, 2020
British Columbia
Hey guys

I've got 1995 5.0 GT. I've had it for 2 years and it's always had a bit of a rough idle, but it's gotten progressively worse. When I say rough idle I mean that when I start it the RPMs rev up to about 1200, then drop to 1000, then drop to about 750. It then proceeds to repeat this process several times before finally settling at an idle around 750, but it doesn't really settle, every few seconds in kinda rumbles and then drops to about 600 RPMs before jumping back up to 750. It also does this little jump every time I put I take it out of park to change it to another gear, and it will do it continually anytime the car is stopped and idling. Also, every once in a while when the engine's cold and I've left home, the first stop sign I come to the engine tries to die, the RPMs drop to almost nothing, but if I hit the gas hard and fast enough she'll keep going. I'm thinking the problem is my IAC but I would love to hear any ideas you guys might have, or if anyone else has had this problem with their stang. I also tried to test the IAC by unplugging it, but even with the engine warm, the engine started and then completely died... don't know if that's normal?

I also made a list of possible causes that have already been dealt with so you guys know what I've already fixed :)
Vacuum Leaks
Air filter
Dirty throttle body
Ignition timing
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5 Year Member
Aug 11, 2013
Cleveland OH Area
An incredibly common problem, and your solution is here:

In general, the idle stop-screw and air-bleed need to be set to allow the car to continue to run (at low idle) with the IAC disconnected. This will largely eliminate the surging idle you're experiencing. Go through the whole check-list, it's time-tested. Some stuff you don't have to worry about for a 95 Mustang - especially getting the TPS voltage exactly correct (our computer adjusts for it). But most of it does.
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