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NicksSticks
NicksSticks, ASE Certified Technician
Category: Car
Satisfied Customers: 1425
Experience:  Ford Drivetrain and Chassis Master, ASE Master Technician
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93 isuzu trooper: engine revs..going down..neutral..DOWN.

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I have a 93 isuzu trooper that sometimes has idle problems. On startup the engine revs up to 2300 rpm or better and will slowly, eventually settle out at about 1200. After putting it into gear and going down the road (it's a manual) I'll put it into neutral at a stop...and that's when the rpm's go UP and DOWN, UP and DOWN, UP and DOWN. I've tried a new idle air control valve and a throttle position sensor already, so I'm not sure what's next. Any ideas?

NicksSticks :

Not going to like this, but if iac valve has been replaced, this is a common symptom of a base engine problem, such as a valve not selaing, allowing air in/ out when not commanded. If no obvious miss fires, time for heads to be removed and rebuilt as neccessary. Sorry for the answer, but it is correct. Thank you!

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NicksSticks :

Not going to like this, but if iac valve has been replaced, this is a common symptom of a base engine problem, such as a valve not selaing, allowing air in/ out when not commanded. If no obvious miss fires, time for heads to be removed and rebuilt as neccessary. Sorry for the answer, but it is correct. Thank you!