Can cleaning it really make a difference? What l mean is if it's caused by a dirty throttle body wouldn't it have to be caked pretty thick to hit 3000 RPMS ? l am not sure of the correct number here but l would guess it should be idling at 900 rpms so wouldn't it take some heavy deposits to make it jump up another 2100 rpms? l could be way off on my line of thinking though so i will give it a try and clean it but if l remember correctly it says not to clean it because it will damage it? Also should note that this engine is a 1995 shortblock with the heads and intakes from a blown up 1996. I also had the heads ported. When l got the engine installed Monday and started for the first time it ran very well but idled at 1100 rpms. I chalked up the slightly high rpms at the time to the pcm relearning since van had sat with a blown engine and no battery from 2005 until I purchased 3 weeks ago so l just hoped that once the pcm relearned the settings that it would correct the idle. Ran fine for 127 miles.
Ran great for 127 miles but on wednesday l started it to go to work and it instantly hit 2500 rpm so l tapped the gas pedal to kick it down but it jumped to 3000 and has been stuck there. l should note that l used the 3 mil. intake manifold gaskets vs the 4 mil. Also not sure l have the cmp sensor set properly,l set it using a Snap on brand multimeter. Also I found 2 loose fuel rail bolts and when l wiggled the fuel rail noticed the injectors moving so could that be casuing the high rpms?
After 3 days of searching for a phantom vacuum leak,testing sensors,checking and cleaning the IMRC and intake manifolds l was truly about to give up for the day and concede defeat at the hands of the 3.8 engine gremlins. l had put my tools away and climbed into the drivers seat of the Windstar to think for a minute before going in to watch the Preakness. l got an idea to try pouring Seafoam into the ldle air control valve and let it soak while l watched the Preakness. When l came back out l hooked the IACV back up and like magic the engine idled perfectly and was running as smooth as ever!! l put 63 miles this evening and it never missed a beat!!
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