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Topic
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’97 Pontiac Trans Sport, 110,000 miles
Car has rough idle, heavy humming, no skips or stumbles when stopped at light, especially after warming up.
Cleaned Throttle Body, EGR, MAF, IAC, checked PCV, no vacuum leaks, air filter is clean; pulled a couple spark plugs/look good. Installed brand new cat and O2 sensors. Fuel filter was changed 2 yrs ago, but car has hardly been driven in that time.
STFT is around -2 when at idle, alternator is putting out 14V. Engine temp is good. No codes on ODB scanner.
When put in Neutral, rough idle disappears, back in Drive it immediately returns like you can feel it engaging.
All fluid levels are topped off and are clean.
Doesn’t affect performance while driving, car runs smooth. I have already read Eric’s article on “Idle Problems”.
Any thoughts?
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Replies
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A couple of things you can check for:
Vacuum leak(s) Hoses, intake manifold, air intake after the MAF
Fuel pressure
Bad fuelCould the idle speed just need to be bumped up a tad?
Also, it may be the coil pack has a crack – that will cause rough idle as well.
GG
[quote=”Capani1″ post=163690]’97 Pontiac Trans Sport, 110,000 miles
Car has rough idle, heavy humming, no skips or stumbles when stopped at light, especially after warming up.
Cleaned Throttle Body, EGR, MAF, IAC, checked PCV, no vacuum leaks, air filter is clean; pulled a couple spark plugs/look good. Installed brand new cat and O2 sensors. Fuel filter was changed 2 yrs ago, but car has hardly been driven in that time.
STFT is around -2 when at idle, alternator is putting out 14V. Engine temp is good. No codes on ODB scanner.
When put in Neutral, rough idle disappears, back in Drive it immediately returns like you can feel it engaging.
All fluid levels are topped off and are clean.
Doesn’t affect performance while driving, car runs smooth. I have already read Eric’s article on “Idle Problems”.
Any thoughts?[/quote]
I only have a few things come to mind. Idle air control valve may have a leak or malfunctioning, the torque converter may be going out as this was what caused it in my car (look for a rumble feeling in third gear between 30 and 40), the dile screw needs adjustment like gginnj suggested, or the tps may need adjustment.
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