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Old Mar 6, 2009 | 03:46 AM
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Unexplained High Idle Problem

The vehicle is 98' E350 5.4 350K miles. It only does it sometimes but when it does get the high idle it makes stopping very hard. I'll throw it in neutral and shut it off otherwise it revs up high well over 2K rpm.
I cleaned the TB, IAT and MAF with no change except better running everywhere but this idle problem. It's not throwing a code which is making this hard to trace. Thanks much, Jeff
 
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Old Mar 6, 2009 | 01:05 PM
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Probably a sticky IAC (Idle air control) could be a vacuum leak but they usually make it idle low.
 
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Old Mar 6, 2009 | 01:10 PM
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Didn't know the 98 5.4 still used an IAC valve. Any idea where its mounted on an E350?
As of right now I test drove it today and it seems to be back to normal idle speed. Maybe the other stuff I did cured it but still worried it may return. Thanks so much for the reply and info!
 
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Old Mar 6, 2009 | 06:11 PM
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Oh you will love it, it is bad enough on an F150, it sits behind the Throttle body, and being a van I bet that is in the depths of hell under the firewall somewhere.
 
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Old Mar 6, 2009 | 08:51 PM
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But we have a removable dog house for whatever can't be reached in front.
 
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Old Mar 7, 2009 | 08:13 AM
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I guess I'll pull the IAC valve off and clean it. It's better but still idles high sometimes.
Any chance the TPS could be bad?
 
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Old Mar 7, 2009 | 02:29 PM
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They go bad also but I've had more issues with the IAC on the modulars, never had a TPS problem yet.
 
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Old Mar 7, 2009 | 06:14 PM
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Cleaned the IAC and test drove it and so far so good. Nice smooth idle and no surging or fast idle anymore.
 
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