High revving 351W
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Joined: Nov 2005
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From: La Grande, OR
High revving 351W
I did a swap in my 1987 F150 a while ago from a blown 302 to a 351W. The 302 was EFI, and the 351W was a 1994 EFI. I switched everything over, and except for some problems that were fixed with the mate-up AOD, I've been happy with it. Except for one thing, whenever I first start it up, the engine holds what seems like an extremely high idle......(900-1200 RPMs?) I don't have a tach though, so i dont know for sure. When I put it in gear though, it comes down to what seems a reasonable idle (500-700 RPMs), and it's fine....however, when I put it back into park and/or neutral, it goes back to the high idle again. since I wasn't having problems with it running, I kept the original 302 EEC Computer, could this have anything/everything to do with the problem? I want to get this fixed, so hopefully some of you guys can help me out. Thanks, and sorry for the long-ish post.
Hotshot
Joined: Jul 2002
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From: Bend,OR
you need to swap in a 5.8/c6 ecu. that is your first starting point. once thats done we can go from there. it should fix the problem though. i did the same swap and really enjoy the 5.8 in my bronco.
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From: La Grande, OR
what about the possibility of a malfunctioning IAC valve? could that make it go high idle in neutral and park, yet not when its in gear. and yeah, i know i need to swap in the right ECU, so that is probably also the problem
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From: La Grande, OR
ok, i got the new EEC module (thanks justin), and it does come down some. I found a tach and put it in and found that with the old EEC, it idles at 2500 RPM, with this new one, it idles in park at 1500 RPM. It still seems too high, there is also some surging, and when I rev it up when it is in park or neutral, the idle doesnt come down, it stays wherever the rev topped out at. anything come to mind?
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Joined: May 2006
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I have this exact problem with my 1990 Econline 351W (stock). I've checked the entire system for vacuum leaks. I even checked the throttle linkage in case it was sticking. I am also ready to focus attention on the IAC. I will keep you informed if this helps.
