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#1
08-29-2009, 02:08 PM
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High Idle at Start?
Do all 4.0's idle to 1500 or more at start and then go down to around 900 to 1000. If I'm in a hurry and don't let it idle down (maybe just 5 seconds) it really jerks the car because of it idling so high. Anyone know if there is a fix for this or is it just the way they are?
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#2
08-30-2009, 04:53 PM
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Re: High Idle at Start?
I'm not sure about most 4.0's, but many cars are programmed this way, to lower emissions. The idea is that the high idle gets the catalytic converter warmed up more quickly, so it starts working faster.
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#3
09-01-2009, 01:09 AM
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Re: High Idle at Start?
4.0's should have an idle flare after being shut off for at least 30 seconds. It should go up and return to normal idle very quickly on a warm engine. This because the iac valve goes to fast idle position upon shutoff in preparation for the next startup.
If yours holds fast idle too long, look for sticky iac (idle air control) valve, or a vacuum leak. Your pcm can't see a vac leak until the o2 sensor heats up enough for closed loop operation. Then it can compensate for small leaks. Worn throttle body shafts can do this too, crack it open slightly and check it for sloppiness.
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