fordork

I have an 88 mustang gt, 5.0L HO, fuel injected...

All of a sudden one day on my way home when i came to a red light, my car idled at like 2,000 rpms. It only does this once i have been driving for awhile and the enigines warm, especially after highway driving. it will idle between 1,800 and 2,000 when in nuetral or with the clutch engaged. if i let it idle like that it will eventually idle down after about 2 full minutes (a long red light) If i shut the car off and start it back up maybe an hour later (but the engine still warm) it wont do it right away. This is very aggravating, annoying and embarassing. Is this a sensor? TPS, or MAP? Has anyone had and solved this same problem? Any and all help is greatly appreciated...

Thank you

U S Marine

I just went though this a couple of months ago. The Coolant temperature sensor was my problem.

fordork

really? I thought maybe the MAP or TPS but i never thought the cts...

???

WhiteFoxGT

If you IAC is good, the TB isnt sticking, and the TPS sensor is within voltage, I'd check for vac leaks..

I just worked on a 5.0 not too long ago at work with a high idle.. I made sure the TB wasnt stuck, the TPS had correct voltage and the IAC was clean as a whistle... I then started spraying 2+2 around the intake (upper to lower area) and the idle would drop dramatically.... found my culprit

U S Marine

You can check the voltage from both of those as well. Check your vacuum lines/hoses for sure as Whitefox said. He has valid solutions. My problem just happened to be a bit obscure, I guess. My idle was more around the 1300 RPM range, and would sometimes go away upon re-start. Speed Density cars act a bit more peculiar when sensors and vac signals start messing up.

fordork

Well i tried cleaning the iac and it idled higher when cold. even with the carb cleaner well burned out of the system. i then unplugged the electrical connector from the iac and it idles better hot, cold, and after a long drive. So i would like to say that the iac is the problem but i dont see why not just leave it unplugged...

U S Marine

I'm still stickin to the ECT. If the PCM thinks the engine is cold, it will run in cold engine mode, like RPM staying high until it's warm enough to atomize the fuel better. The ECT is a pretty vital part of a Speed Density system. There is a test for it in a Haynes manual, if I'm not mistaken. It's a resistance test over varying degrees.

WhiteFoxGT

Replace the IAC and ECT, call it a day? lol

U S Marine

Sounds like a wrap!