Rough Idle

Fuel filter? Have you tried 93 octane and fuel injector cleaner? Clogged cats? New coil packs or have them tested?

Idle air control. Mine kinda studder at 1500 rpm or 45 to 50 mph. Like a swoosh sounds.

Btw mine were cracking too. Tome for new ones bud. Motorcraft or msd off american muscle. Everyone says motorcraft, I have accel cause o reilly never has anything in stock.

Msd is on sale on AM, when's the last time you changed 02 sensors?

MPScott1 said:

I Since my last post i replaced the IAC but still having issues. Just sitting in my drive way with the car in neutral i revved it to about 2500 RPM and pushed the brakes, the rpms dropped down to almost 500 and the engine was idling real rough, when i released the brakes the RPMs went back up. So i have no idea what the issue is,

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^^^ The RPM's dropping when pressing on the brakes is a function of the hydro-boost. The power steering pump is applying a load to the motor.

FWIIW, most any motor will run rough if the idle is too low.

Consider that the Mustang's does not take power steering load into consideration when adjusting the idle. It's normal for the idle to be slightly low when setting at a stop with your foot hard on the brake.

It's also normal for the idle to "hunt" slightly due to a rapidly changing idle motor load. That is the IAC doing it's job.

The difficultly here is separating what's normal from what's not.

IMO it's normal for the idle to drop when standing hard on the brakes at a stop. But the idle should return to normal levels after a short while. This indicates that the IAC is doing it's job. What would help the trouble shooting is to "know" what the IAC duty percentage is and to see how the PCM is changing it. An ODB2 scanner is needed for this.

Regarding the COP boots. It's possible to buy a complete set of just the boots for less $$'s than the cost of a single COP. Check out Autozone (Duralast).

Has the battery and alternator been tested? Are the battery cables clean and tight? Don't cut corners here. Almost all auto parts stores will test both for free.

How does the car drive when moving? How's the gas mileage? If both are good, them maybe the ignition system is OK. And maybe some other "adjustments" are needed. Perhaps up to and including the "driver mod".