MAF, AIC, TPS.... WTF?

[Last5.0Cobra]

About two weeks ago i was parking my car at school, and it started to idle weird. I shut it off thinking maybe the timing had gotten off somehow.... Anyway, when i started it back up it did it again. It would rev to about 1400 rpm then drop to 800. Over and over and over. I hit the gas... and it stopped. Two days later it started again. I don't always drive her everyday. Anyway, i took it to the local mustang shop... they know what they are doing. While i didn't schedule an appointment the owner hooked up the diagnostic machine for me. It threw an AIC code. So we ordered a new one. Last weekend i put in a Spec clutch, and Fidanza flywheel. Two days later i put the AIC on.... and it did it again. He took the part back, and we hooked it up to a diagnostic reader again. This time.. the code was low voltage to MAF. Weird, huh? A few days later i drove it to Schmuck's for a simple alternator test. On the way, she started to rev up uncontrollably to as high as 5000 rpm. Which is disconcerting when shes in gear Anyway, the alternator is fine. But now it threw MAF, AIC, and throttle position sensor codes. Throttle position... no S! Anyway, i am extremely confused. I made a real appointment with the Mustang shop... its for June 2. So i have until then to figure it out... or it is going to cost me $83 and hour. Yesterday, i did change the spark plugs, and inspected the spark plug wires. So anyway, i am fairly sure that it is wiring.... but am not sure where to start... or how. Any ideas at this point are good ideas. Thank you in advance for all of your responses.

 

[HISSIN50]

If you shut the car off and restart it, does it idle normally for awhile? Then when it acts up again, if you repeat this, does it idle normally for a little while? If so, the TPS is likely.

Otherwise, I'd start going over vac lines.

Did the shop tell you what duty cycle your IAC was seeing during low and high idle periods?



Good luck.

 

[Last5.0Cobra]

Yes it did act normally when i shut it off, and turn it on, now it revs to like 4000 rpm when i turn it on. Not sure what you mean by duty cycle... it was reading -40 degrees for awhile?

 

[WhiteCobra95]

Sounds like a bad ground or a shorted 5V sesnor supply. I would suggest starting up the car, get under the hood and LIGHTLY rattle the wiring harness in several places. If anything changes, idle speed - rough running, then it's probably a short or broken wire. In any case it's not going to be easy to find.

 

[HISSIN50]

When it revs higher than normal, I'd disconnect the IAC's electrical connector and see if the idle returns to normal. You either have an IAC issue or a massive but non-constant vacuum leak.

Don't worry about the duty cycle stuff (it relates to how hard a device with a cyclic function works).