JR, MY, JT.. Question about IAC...

stang8urimport · Dec 17, 2005

Got a question. How many volts should be going to the IAC. My car keeps wanting to stall when I push the clutch in. I replace the IAC with a geniune Ford part (110 bucks!!) and it still hasn't fixed my problem. Also, if I disconned it.. it does nothing different. Same idle, same driveablility. It is brand new like I said, and I replaced it because of this problem... I figured it has 103,000 miles on it and I might as well replace it. So how can I test that it is actually working properly? I had the idle set at 650 RPM with it unplugged and it would die all the time, esspecially with the a/c on. I upped the idle to about 850, and it STILL does it. Soooooo help? Voltage at the iac should be? Which wires to test... How do I know it is actually working? Thanks a bunch guys.

Nick

90mustangGT · Dec 17, 2005

Well, I would tell you, but since you want the answer form those guys...

J/K I am pretty sure it is a 5V reference. What does your TPS read at closed throttle? It should read about .99V.

HISSIN50 · Dec 17, 2005

Look for 12 volts at the red wire (who woulda thunk).
The puter pulses ground IIRC to create the duty cycle/pulsing. I think you need to measure the square wave to check function of the IAC itself. That is beyond most of us at home..........

Wait, Nick - check JR's sticky on idle surging. He runs down some basic IAC testing right near the top of his first post on page one.

He covers the stuff WAY better than I can.

Good luck Nick.

90mustangGT · Dec 17, 2005

HISSIN50 said:
Look for 12 volts at the red wire (who woulda thunk).
The puter pulses ground IIRC to create the duty cycle/pulsing. I think you need to measure the square wave to check function of the IAC itself. That is beyond most of us at home..........

Wait, Nick - check JR's sticky on idle surging. He runs down some basic IAC testing right near the top of his first post on page one.

He covers the stuff WAY better than I can.

Good luck Nick.

Oh ****, I keep thinking about the TPS sensor for some reason. Your right JT, the IAC uses steps to close and open the IAC plunger. I'm not sure about actual old ford systems because most of what I work on is so much newer, so maby it is 12V, but 5V is usually what the computer sends out. Most IAC's are not solonoids such as a fuel injector, but just motors such as a window motor. The IAC usually closes at speed, if your speed sensor is bad, that could be a problem. Also, MAF sensor output can also effect the IAC control.

jrichker · Dec 17, 2005

Ford was cheap - the IAC is a 12 volt solenoid on the 5.0's.

The IAC can only add air to increase the idle speed. It cannot subtract air and reduce the BASE idle speed. That's why some guys replace the IAC and the idle doesn't change. The mechanical base idle setting needs to be set below 625 RPM to get the IAC working to add air to increase the idle speed to the factory level. Sometimes there are other mechanical/computer/electrical problems that make getting the engine to idle at 625 RPMs almost impossible.

stang8urimport · Dec 17, 2005

k, well I got a scanner at Autozone and will check codes tomorrow, then check voltage at the IAC. I'll let you know what happens tomorrow.

JR, MY, JT.. Question about IAC...

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