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