Mach 1 Hanging Idle

[twogts4us]

Yep, that's the problem, a hanging idle, especially when it's cold - any fixes? This is on my new ride, a 2004 Mach 1. I just got done installing (and then removing) an IAC restrictor plate (homemade gimmick, using two holes, one was the standard size, the second one, on the pass side of the IAC, was smaller, about 9/32", (all cut and drilled as described in an article here on StangNet). It seemed to drop the idle quicker in between shifts, but the idle, both cold and warm, was worse than ever...hanging around 1500 RPMS!
Help!

 

[hotrodnut]

I have it too, I have the IAC plate installed, diablo tune like yours but it still hangs, It usually hangs at about 1000-1100 though for a few seconds before dropping to normal idle speed.

It's bugs me that it does it, I wrote to diablo a long while ago asking if they could send me a tune that would eliminate it but never got an answer so I assumed they couldn't.

When I drive the Mach steady for several miles and come to a stop it doesn't happen, but short trips and rips around town it always hangs.

 

[Mach1Run]

Mine hangs once in a blue moon but that was a known issue with the accufab TB i installed I believe.

 

[hotrodnut]

There was a SPECIAL SERVICE MESSAGE dated in 2003 that said that some Mustang Mach1s may have an intermittent high idle. It was caused by a damaged wiring harness that was on the left side near the rear of the transmission crossmember and mount. I think it was the connector or something rubbing.