Idles high on start up - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 10-05-2005, 03:42 PM
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Idles high on start up

First post for me here. I have a 1989 Bronco 302. I had the motor rebuilt about 5000 miles ago. Bored it .10 over, flat top pistons, shaved the head a wee bit, long headers, and dual exhaust. Went back with a stock cam. No emmissions whatsoever. Well, unless you include the EGR valve. That's about it. Anyhow, it has recently developed the annoying trait of idling high on startup, especially when cold. It goes up to 2000-2300 rpm and eventually comes down to around 1100. It will do this even when warm for the most part. This is my first Bronco and my second car with a computer on it, so I am at a loss on how to go about diagnosing the problem. Could it be that the engine has just broken in and loosened up a bit and it may just need idling down? Is that common?

I have checked for vacuum leaks and found none. The truck and motor run better than ever. Smells a little richer than I like, but the plugs indicate a near perfect burn. My gas mileage is about 13 mpg no matter how I drive it. I suspect it should be better than that. Thank goodness it can run on 87 octane if it has too. No pinging at all. I don't know about error codes, but am clueless there. I'm sure with all the emissions removed their might be a buttload of those to sift thru anyway.

I guess the thing to remember is that this just started about a month ago. Otherwise she has and is still running like a champ with the exception of this high idle. Thanks in advance for any help rendered.
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post #2 of (permalink) Old 10-14-2005, 12:43 PM
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Re: Idles high on start up

I had the same problem on my 95 Bronco. I tried changing the idle air control valve but that didnt help. I got a 121 when i checked my codes which indicated i had a problem with my throttle position sensor. I checked the voltage on it and it was 1.5 volts idle when it should be <1V. I replaced it and that fixed my problem. the new one is at .9V idle which gives me between 800-1000rpm. Before i would be lucky if it dropped down to 1100rpm idle. Hope this helps.
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