ECM strategy qs.
Post Fiend
Joined: Apr 2005
Posts: 5,720
Likes: 5
From: Washington state
1. intermittent intake air leak
2. intermittent MAP or MAF sensor output
3. intermittent false signal from pwr steering switch or AC on switch
what's your O2 sensor V. reading doing during idle rpm increase periods?
2. intermittent MAP or MAF sensor output
3. intermittent false signal from pwr steering switch or AC on switch
what's your O2 sensor V. reading doing during idle rpm increase periods?
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Post Fiend
Joined: Oct 2005
Posts: 5,242
Likes: 0
From: Kiev, Ukraine
I will try to measure. ECM increases idle speed for 5-20 sec. only. May be canister purge solenoid does it
Lead Driver
Joined: Sep 2003
Posts: 7,016
Likes: 209
From: SoCal
Besides the air leaks, any false signal that causes the EEC to advance the timing will cause engine rpm to surge. That's easy enough to check with a timing light. You don't even have to find a real mark, just a reference point, and see if the timing changes when the engine surges.
Also, the EEC uses the IAC to bump up engine speed when running AC. If he's unplugged the IAC, that should no longer happen.
Also, the EEC uses the IAC to bump up engine speed when running AC. If he's unplugged the IAC, that should no longer happen.
Elder User
Joined: Dec 2006
Posts: 830
Likes: 0
From: Kitchener,Ontario,Canada
Pretty sure the Cannister purge operates at 1500 RPM's or more, but if it does operate at idle, it could make a fluctation. I would disconnect & plug the purge line with your thumb & see if you can feel a vacuum. Do you have an intermittent sticky PCV ?
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timbersteel
1987 - 1996 F150 & Larger F-Series Trucks
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Jul 24, 2013 06:12 PM
