How does A/C affect idle controls?
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Joined: Sep 2000
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How does A/C affect idle controls?
The last few summers my idle has been affected when I put the a/c on. The problem just reoccured. It runs smooth normally, but when I put the a/c on the idle drops.
At first, the idle is fine with the a/c on (700 - 800 rpm. After the car runs for a while the idle seems to kick out and will drop to around 300 - 400 rpm. When I turn the a/c off the idle returns to normal (back up to 700 - 800 rpm). What is making it drop with the a/c on?
The manual shows terminal 33 on the fuel injection control unit gets a signal when the a/c is on (right off of the a/c ON switch). I am thinking about disabling this signal to terminal 33. If it idles fine without the a/c on, then the ISV should control with the a/c on. Maybe there is a short in signal 33 to the fuel injection control unit and I won't see any difference.
Any help in diagnosis of this problem would be appreciated.
Thanks, Walt D
1988 Audi 90 5-cyl
192,000 mi
At first, the idle is fine with the a/c on (700 - 800 rpm. After the car runs for a while the idle seems to kick out and will drop to around 300 - 400 rpm. When I turn the a/c off the idle returns to normal (back up to 700 - 800 rpm). What is making it drop with the a/c on?
The manual shows terminal 33 on the fuel injection control unit gets a signal when the a/c is on (right off of the a/c ON switch). I am thinking about disabling this signal to terminal 33. If it idles fine without the a/c on, then the ISV should control with the a/c on. Maybe there is a short in signal 33 to the fuel injection control unit and I won't see any difference.
Any help in diagnosis of this problem would be appreciated.
Thanks, Walt D
1988 Audi 90 5-cyl
192,000 mi
Junior Member
Joined: Mar 2000
Posts: 675
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I think most likely the ISV is dirty...
I think that most likely, but I have also had trouble with the idle switch on the throttle stop being dirty. The car just doesn't turn the idle circuit on. Good luck with it.
AudiWorld Expert
Joined: Jun 2000
Posts: 29,356
Likes: 1
Re: How does A/C affect idle controls?
Idle is actually suppose to raise when the a/c is tuned on due to the load the compressor demands of the engine.
Your system sounds like its not working at all!
My 88 90 kicks the idle up 200 rpms when a/c is turned on.
Your system sounds like its not working at all!
My 88 90 kicks the idle up 200 rpms when a/c is turned on.
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