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1988 Audi 90 idle oscillation

  #1  
Old 07-05-2005, 02:46 PM
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Join Date: Jun 2005
Location: Canada
Posts: 32
Default 1988 Audi 90 idle oscillation

Greetings all, I am investigating the following:

Vehicle: 1988 Audi 90 4 cylinder. New Plugs, Plug Wire set, Distributor cap. No (apparent) vacuum leaks, good gas mileage, Clean ISV, most connectors disassembled, cleaned.

When car is warmed up, idle oscillates between 800 and 1200 RPMs about once a second. When this occurs, the control voltage to the ISV drops from about 4.0 (average DC reading, actual signal is AC) to zero. This allows the ISV to mechanically oscillate from closed to open resulting in the idle oscillation. I have thoroughly cleaned the ISV, and it works perfectly until after warm up. This suggests a bad sensor signal/connection telling the ECU to stop controlling idle ??? The temperature dependence has less than 100% correlation, but close.

Any insights, similar experience data would be helpful and most appreciated.


Thanks, Ian.
 
  #2  
Old 11-18-2006, 09:58 AM
1st Gear
Join Date: Nov 2006
Posts: 9
Default RE: 1988 Audi 90 idle oscillation

IT COULD BE YOUR AIRFLOW METER AND FUEL DISTRIBUTOR
 
  #3  
Old 12-05-2006, 05:36 PM
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Join Date: Nov 2006
Location:
Posts: 5
Default RE: 1988 Audi 90 idle oscillation

agree as above, also does the throttle cable get warm and stick open as mine did on my 80 2.0 sport?
sensor should not be too much either no more than £60.00.
 
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