[93BlkMustangGT]

I would reset the base idle using the usual methods. When coming to a stop, i depress the clutch and the RPM's jump to around 1800rpm. At a full stop, the RPM's will drop where I want it- 850rpms but not after hanging at high RPM. The Idle Bypass Valve is clean; Throttle Body is clean; the air-idle spacer thing has no effect. TPS is at 0.98volts and a recent dynotune says that all settings is where it should be.

I've done everything yet nothing seems to work.

I also cleaned the MAF element. One of the elements has a darker color than the other. I use almost a full can of throttle body cleaner on the darker color element but no change. I assume that it's clean despite the darker color.

The idle is irratic and it sounds as if it will die.. almost spurring. At 850rpms the idle should almost be rock solid but this is not the case.

I am suspicious my of alternator, a Power Master (the Black one). I think it puts out 130A. When i turn on my dual electric fan, the overall power drops slightly. Is there a way to test it?

At this point i'm believe that the problem has to be a bad part

 

[93BlkMustangGT]

Yes... I have sprayed the MAF wires. One appears to be slightly darker (brownish) than the other. I used a q-tip and lightly brushed it along with the other wire and gave both another dose of TB cleaner.

On a hunch, i bought a new Idle Bypass Valve and went through the reset procedure. I then started her up with the Idle Bypass Valve unplugged and it was aweful, at first. A few turns of the idle stop screw and it stablized. I then adjusted idle to where i want it (850rpms) and let it idle for a while.

During this time, the idle rests at 850rpm and then builds up to around 1500rpm then back down to 850, then back up at 1500... etc.

I do let it do this until it stablizes? or will it stablize when the Idle Bypass Valve is connected?

 

[93BlkMustangGT]

I went to a muffler shop yesterday, bad idle and all, and the mechanic found a header leak at the passenger side at the gasket & a leak on the header itself right above the collector.

I want to get this idle problem resolved before the new headers come in.
New headers will be JBA Titanium Coated 1 5/8 shorties back ordered until first week of November.

edit: i started up the car this morning. Cold starts has been very ugly as of late. I would have to hold the engine for about 20 seconds at 2000rpm or else it would just die out. The engine is warm and appears to be idling correctly. I take the car out and the high idle is back. When shifting, it sounds as if i do not let go of the gas pedal. RPM stays high. Coming up to a stop RPMs are at 1500-2000. Sometimes it will drop and idle somewhat correctly but then it will do the same thing as described.

Fustration is mounting.

 

[93BlkMustangGT]

Quick review, please. How to do a vacuum check... No really... That's one thing i did not check and do not know how to do.

I finally got the car to idle somewhat steadily, this morning. The RPM's now behaves normally when shift gears and the idle surges only a few hundred RPMs.

Ready for the weird part? The idle rests at 850, right where i want it. But now, after a few minutes, the idle will drop to around 700 hundred or so, as if the car will stall. I would then have to press on the gas pedal to bring up the rev's. The engine will idle normally and then would drop again after a few minutes.

Any thoughts?