A guy at work is looking to buy a 99 mustang GT with 82k miles for about $5,000. Apparently the only issues with the car are the A/C needs a recharge, and the RPM's don't drop right away when the clutch is depressed. Apparently when he was test driving it and was revving a little bit with the clutch in, the RPM's very slowly drop for a couple seconds, then go all the way back down. Has anyone heard of this and are there any serious issues? I have an 06 Mustang GT and sometimes the revs took a bit longer to drop before I had my tunes, but it was mostly when the engine was cold.

Your insight is appreciated.

 

Is it throwing a code? It could be the idle adjuster on the bottom of the throttle body is not set correctly. Also, these cars dont drop hard right away when you push in the clutch, they hang just a bit. Its possible its just the normal setting and he is used to a carb'd car.

 

I had him hop into mine and he said mine doesn't hang at all compared to the 99, then again, I do remember it hanging more before I tuned it. I don't think it's the idle adjuster because he said it idles just fine, it just takes awhile to get down to it.

The car used to have a chip on it, but the owner pulled it and sold it. I don't know if this generation had as advanced of a computer as the new ones that drive by wire and adjust to driving styles.

 

The IAC is a prime suspect for hanging revs. When you throttle the car up on a 2v 4.6 it will slowly creep its way back down to idle because of a restriction the IAC is putting on flow.

See this for more info:
https://mustangforums.com/m_2625353/tm.htm