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Idle Questions

In message <199705091453.KAA18999@cdc3.cdc.net> "Jeff Wolf" writes:

> A few weeks ago I wrote to you all about my buddies '88 5000cstq that would
> only idle high.  As per your suggestions we checked the Throttle position
> switch and it seems to be fine.  We also cleaned the ISV and that seemed to
> fix the problem but only very temporarily.  After 4 or 5 revs, the engine
> idles from 2200 to 2800 RPM.  

a) A number of things cause the controller to force idle to go high.  One is 
   low battery voltage, another is the a/c.
b) The ISV is directly controlled (both wires) from the controller.  If this
   circuit is interrupted, the ISV is disabled until the ignition is switched
   off for at least five seconds.  You may have an intermittent break in the 
   wiring to the ISV.
c) The _only_ way to test the ISV is to put amps through it - it is 
   half-actuated at 430ma.  A 3V battery across the terminals should produce a
   visible movement of the plunger.  You'll need 6V or more to get full 
Some cars have in-situ diagnostics.  If there is a fuse holder on top of the 
fuel pump relay, insert a fuse and switch on the ignition.  If the fuel pump 
starts running after four seconds, you have the feature.  Pull the fuse, and re-
insert for four seconds.  Repeat.  You will find that the components that can 
be addressed by the computer will be activated in turn - the cold start 
valve, the fuel frequency valve, the wastegate frequency valve, the ISV, etc.  
The order varies, and not all cars with the feature will drive the ISV.  Mine 
doesn't.  If your friend's drives the ISV, take it off and look at the plunger 
- it should be moving across its full range of travel.  If you can get it 
"ticking" this way, give the wiring harness a good kicking.  If it stops, 
you've found a break. 

 Phil Payne
 Committee Member, UK Audi [ur-]quattro Owners Club