Fixing Fox Body Mustang Rough Idle Like a Champ

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Youtuber gives a great breakdown on how to smooth out your engine timing if you have a custom cam.

For the most part, a Fox Body Mustang is an easy car to upgrade and maintain. They’re relatively simple rides that anyone with basic wrenching skills can keep going for a long time. But like any old car (yea, they’re pretty old now), the Fox Body Mustang has its flaws. One of those minor setbacks is a rough idle, something many owners are quite familiar with. Thankfully, Youtuber BREW2L was happy to share this detailed video on how to fix this common problem.

The owner of this 1989 Mustang GT picked it up with some go-fast goodies already in place. But the engine bay is kind of a mess, and it wants to stall out at idle. Part of the problem, right off the bat, is the idle screw. “You have to be careful with these idle screws,” our host notes. “Because when you turn them, you’re effectively changing the TPS.”

Foxbody Mustang Idle Issues

The first step in correcting this issue is setting the timing. And it turned out that this Mustang was set a little too high, at around 14-15 degrees. So our host knocked it back to around 10 degrees and moved on. The TPS checks out OK, so he demonstrates how big of an effect the idle screw has on things. “If you were to turn it just a little bit, you can see that it changes the TPS.” Quite a bit, in fact.

Foxbody Mustang Idle Issues

With the car running, our host plays around with the idle screw and lowers it to the point where it’ll barely run on its own. He then runs a smoke test, which goes amazingly well with no vacuum leaks. After a full base idle reset, he toys around with the idle and double checks everything.

Foxbody Mustang Idle Issues

With a little more fine tuning, this old Mustang is idling like a champ. So if you’ve got similar problems, here’ a great road map on how to get your pony running smoothly.

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Brett Foote has been covering the automotive industry for over five years and is a longtime contributor to Internet Brands’ Auto Group sites, including Chevrolet Forum, Rennlist, and Ford Truck Enthusiasts, among other popular sites.

He has been an automotive enthusiast since the day he came into this world and rode home from the hospital in a first-gen Mustang, and he's been wrenching on them nearly as long.

In addition to his expertise writing about cars, trucks, motorcycles, and every other type of automobile, Brett had spent several years running parts for local auto dealerships.

You can follow along with his builds and various automotive shenanigans on Instagram: @bfoote.

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