Engine surges when a/c cycles off
Posting Guru
Joined: Feb 2002
Posts: 1,534
Likes: 2
From: Warren, MI
When the computer commands AC compressor operation (compressor clutch operation is moderated by the PCM under software control), it also issues a leading command to the IAC to open more to compensate for the extra load the compressor places on the engine.
When the compressor is disengaged, the PCM removes the "extra" bias from the IAC control circuit which should allow the idle speed to drop back to normal. If the IAC, for example, is sticky, it will remain in the position that allows too much air past the throttle plate and will cause higher RPMs or loss of idle speed control.
When the compressor is disengaged, the PCM removes the "extra" bias from the IAC control circuit which should allow the idle speed to drop back to normal. If the IAC, for example, is sticky, it will remain in the position that allows too much air past the throttle plate and will cause higher RPMs or loss of idle speed control.
Logistics Pro
Joined: Jan 2002
Posts: 4,907
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From: suburban atlanta
If it were mine, I'd be finding another IAC to fiddle with. If the IAC can control idle under unloaded conditions, i.e. with the A/C deactivated, it should be able to do so after the A/C has been run, and then deactivated. It does not do so. No air leak will come and go with the A/C control... so, the only thing that has been 'commanded' is the IAC, and it is not responding, apparently.
tom
tom
Posting Guru
Joined: Feb 2002
Posts: 1,534
Likes: 2
From: Warren, MI
If it were mine, I'd be finding another IAC to fiddle with. If the IAC can control idle under unloaded conditions, i.e. with the A/C deactivated, it should be able to do so after the A/C has been run, and then deactivated. It does not do so. No air leak will come and go with the A/C control... so, the only thing that has been 'commanded' is the IAC, and it is not responding, apparently.
tom
tom
OP: What happens if you turn off your A/C when your above idle speed or while still driving then coming to idle speed?
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ewgoforth
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
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Sep 15, 2007 03:38 PM
