Motor idles 2-3000 runs rough ONLY after hot starting - Ford Mustang Forums : Mustang Forum
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post #1 of 2 Old 05-03-2015, 12:46 AM Thread Starter
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Motor idles 2-3000 runs rough ONLY after hot starting

This started a while back after I had batt unplugged w/o O2 sensors. Since then I've installed new sensors and done the base idle reset a few times. When I start up in the morning or after the cars been sitting for 3+ hours it idles smooth and runs normal. If I start it up after anywhere from a quick beer store run up to an hour run through the hills, it runs smooth for 5-10 seconds then the idle jumps upwards of 2-2500 rpm and hangs for about a minute. I'll drive the car and if i mope around the idle will drop down to normal. If I'm romping on it or are anywhere over half pedal when the idle goes to drop it will sputter and backfire and the smell of gas is overwhelming. I've found if I yank the plug at the iac motor the idle drops. No other codes than all the emissions stuff that's deleted. I'm curious what would cause a signal at the iac to skyrocket the idle then boom, drop back down. Thanks for the time and any input is appreciated! -Derek

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post #2 of 2 Old 05-03-2015, 08:59 AM
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either the IAC is commanded to do what it is doing, or it is sticking open, or there is leakage to ground on the ground side, as the solenoid is a ground switched duty cycle.

therefore a ground can keep it wide open.

if there is a command, you will need to scan the ecm while it is doing it.

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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