Re: Idle Questions

[Andrew Duane USG/PE <duane@zk3.dec.com>]

Hairy green toads from Mars made Jeff Wolf say:
> 
> I have a couple of questions regarding some poor idleing.
> 
> 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.  

This sounds like the problem I finally tracked down on my '89 100Q.

I thought the ISV was bad, or there was a leak, or the screw was gone.
I even thought the throttle body might be shot.

It turned out to be the dashpot spring/plunger in the throttle body.
It was slightly corroded, and sometimes wouldn't let the throttle
body close all the way at idle. My car either idled right, or at 2800.
I just pulled the spring and plunger out, the car works fine for 4 years.


> Now for some help with my car :)  I own an '89 100 (no turbo or quattro). 
> The car runs and idles fine except when idleing with the air conditioning
> compressor on.  when this happens the idle drop to about 550-600 rpm
> resulting in a very rough running engine.  Could this problem be caused by
> the Main idle adjustment (is there such a thing on my car?) being set too
> low so that even with the ISV compensation the idle is still too low?  Can
> I just disconnect the ISV and see where it normally idles?

It won't really idle with the ISV unplugged. It sounds like the ISV control
signal is not getting the boost from the A/C circuit. Could be bad wiring,
a bad ISV, or a bad connection.


-- 

Andrew L. Duane (JOT-7)			duane@zk3.dec.com
Digital Equipment Corporation		(603)-881-1294
110 Spit Brook Road
M/S ZKO3-3/U14
Nashua, NH    03062-2698

Only my cat shares my opinions, and she's too heavy to care.