5.0L (1979-1995) Mustang Technical discussions on 5.0 Liter Mustangs within. This does not include the 5.0 from the 2011 Mustang GT. That information is in the 2005-1011 section.

IDLE PROBLEM

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Old May 17, 2005 | 07:18 PM
  #1  
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tomabram
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Default IDLE PROBLEM

My car is a 88 GT. I have tried to reset the idle several times. It still idles too high. When I disconnect the IAC the idle comes down to where it should be. I can turn the idle down to where it should be with the IAC connected but the butterfly catches on the TB. The lowest I can get the idle is about 1200 without it catching. Anybody else have this problem? Any help would be greatly appreciated.
Also, the IAC is new.
Thanks
Old May 17, 2005 | 07:29 PM
  #2  
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stanglx2002
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Default RE: IDLE PROBLEM

have you cleaned the tb to make sure there isnt any crap in there that wont let the idle come down
Old May 17, 2005 | 08:38 PM
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Default RE: IDLE PROBLEM

TB is brand new and clean.
Old May 17, 2005 | 08:40 PM
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Default RE: IDLE PROBLEM

Sounds like a vacuum leak. When I was working on my car and forgot to put a vaccum plug back on, the idle wouldn't come down, below at about what you're saying. Since your 88 , it's speed density and looks at vacuum to see how much the engine is under load. when the MAp sensor sees lees vaccum, it thinks the engine is at more RPM and more of a load, don't ask why it doesn't look at RPM vs Vaccum at idle, 80's technology... thus the higher RPM at idle.
Old May 17, 2005 | 08:42 PM
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Default RE: IDLE PROBLEM


ORIGINAL: 86HOGT

Sounds like a vacuum leak. When I was working on my car and forgot to put a vaccum plug back on, the idle wouldn't come down, below at about what you're saying. Since your 88 , it's speed density and looks at vacuum to see how much the engine is under load. when the MAp sensor sees lees vaccum, it thinks the engine is at more RPM and more of a load, don't ask why it doesn't look at RPM vs Vaccum at idle, 80's technology... thus the higher RPM at idle.
i agree look for a vaccum leak
Old May 17, 2005 | 08:49 PM
  #6  
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Default RE: IDLE PROBLEM

Ok thanks, but when I disconnect the IAC it idles perfect. And I can still get it down with the screw but the butterfly catches. Can this still be a vacuum leak?
Old May 17, 2005 | 09:38 PM
  #7  
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Default RE: IDLE PROBLEM

I think I got it. I put in the IAC restrictor plate with a 5/32" hole. Then reset the idle and disconected the battery. Now it idles at 800-900rpm without the TB butterfly catching. Hope the idle holds.
thanks guys
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