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Discussion Starter #1 (Edited)
Hello, this is my first post. I'm glad I found you folks.
I need some help finding the cause of a fast idle. The buggy, a 2001 JCG with about 160K miles, 4.7L V8, is idling at about 1200 - 1400 rpm. I can't find any air leaks. I've replace the IAC and cleaned the IAC area. If I block the IAC inlet (with the throttle plate closed) I can stall the engine, so I think the air that's causing the fast idle is getting in through the IAC inlet. On the OBD-II scan tool, the MAP sensor is reading from 26 to 30 KPA. Is this a normal reading? Also, I'm not getting any error codes. And no check engine light. Sometime the idle isn't steady - it pulses down to 800 - 1000 rpm or so. Once in a while it will drop down to the normal 600 rpm and stay there until I shift into gear or bump the throttle. I don't know if any other sensors have an effect on the IAC position. Suggestions appreciated.
 

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Discussion Starter #3
Bingo!

A new TPS and the machine is behaving again. The TPS readout on the scan tool had looked reasonable to me, but when I unplugged the sensor connector and checked the TPS with an analog ohmmeter it seemed like the pot was a bit noisy around the idle position. I'm not sure why the IAC would be responding to the TPS output (if, in fact, that is what is happening) but now all seems to be okay.
 
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