audilong

My 84 5000S starts great, idles about 1500 rpm but only for a very short while and then the idle speed drops abruptly to about 500-600. What cuses this?
It slowly then goes up to 850 as the car warms up. Have had the car for 16 years.

comp_jas

I've been trying to figure out the same on my car. I think there is a vacuum leak but I can't find it.

Boost is also 1.1 to 1.2 max.

tradewynne

I have a similar problem, but it's erratic and it sometimes occurs even when it's warm. Idle speed on start-up drops to 200+/- one day, then it's fine the next. Engine light comes on coasting down hill in gear, and then goes off as soon as I touch the gas.

The problem is never there AFTER restarting when
it's warm, but it has persisted BEFORE restarting for 20 minutes+.....

BW
'87 5000CS TQ

DanA100

It is normal to have higher Rpms when the car is cold. Nowever, i they are fluctuating and not stable, going up and down with no reason, i would suspect the Idle Stabilizer Valve (ISV). It should be removed and cleaned(soaked) very well in carb cleaner.

tradewynne

"i would suspect the Idle Stabilizer Valve (ISV). It should be removed and cleaned(soaked) very well in carb cleaner."

THANKS! Very much, will do. I should have also mentioned < 5K on plugs, wires, distributer, etc.

BW

DanA100

Yeah, doesn't sound like an electrical problem.
Just try the ISV first and clean it really well....soak it in carb cleaner for an hour or at least spray it very very well!

audilong

Where is the ISV on 5000S so I can clean it?

86_5K

Here is a picture of the ISV and you can find more information <a href="http://www.humanspeakers.com/audi/isv.htm">here</a>.

<img src="http://astro.uchicago.edu/~mzm/personal/jpg/isv1.jpg">

I steal the picture from Huw's site, by the way.