TPS symptoms...

Sexton66

New member
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After we finally got warmer weather my 94 has started idling erratically, revs up and down perhaps 5x a minute in coincidence with engagement of the HVAC compressor. Starting & performance is fine, fuel economy remains excellent. IAC I replaced 2 years ago (might clean to see if that has an effect), no CEL. OBD 1 readers are scarce around here, anyway last time I did have it read, was told the computer wasn't communicating. No big deal there. It's not a drivability issue yet, so insight would be appreciated.
 

YoungOldMan

Member
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Could be a bearing in the compressor pulley. It takes a lot of power to run that compressor, so some change in idle reva would be expected, but if the revs are jumping way up reliably and consistently when the compressor engages I’d suspect a mechanical issue
 

Town

Senior Member
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Ottawa Ontario Canada
Is the engine speed stable in park without accessories in use? Does the engine surge when you put it in drive but stay parked? If it surges in drive then likely the IAC, cleaning does not work, so get a Motorcraft IAC. If the surging only occurs with A/C compressor operation then that would be unusual. The IAC should be able to cope with a consistent load from the compressor, so perhaps the compressor is cycling as part of another problem, and the IAC cannot cope with a quickly varying load. Have you listened to compressor with hood up and A/C engaged in Park and engine running.?

The problem TPS will typically cause a pause in acceleration off idle and as you apply more throttle the car wakes up and accelerates. The pause is due to the resistance of the TPS going to 0 instead of gradually increasing as the throttle is opened. It can also cause a loss of speed at your typical cruising speed, again due to erosion of the resistance material in the TPS.
 

Sexton66

New member
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Well informed responses! Thank you, I'll look into it this weekend. IAC is not making the moaning sound I've experienced in the past and the compressor is original, I've only had to recharge the system once since I've owned it (6 years) so it wouldn't be too much of a surprise...
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Sexton66

New member
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I cleaned the IAC, replaced the air filter and it seemed to alliviate the problem, but I've only put 80 miles on it since. Fuel filter is due but I'll wait until it warms up a bit more as the unit runs just fine now.
 
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