Idle and a/c
 

My 88 Carrera normally idles at 800 rpm, but with a/c on the idle drops to 600 and it gets rough & lumpy. Is this normal, and if not, what do I do about it?

I don't know if it is normal, but my '83 SC does it too.

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Robert Stoll
83 SC
83 944

In my Ford pick-em-up truck, some little gizzmo kicks up the idle speed every time the a/c cuts in. The Porsche a/c is pretty crummy, but shouldn't it have something similar?

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'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
The Blue Bomber's Website

I believe the '88 (and my 85) have an Idle Speed sabilizing valve, or an ISV.

I am not sure how to go about checking it, but it sounds like yours is not working.

When I turn on my a/c my RPMs actually go up about 50 rpm (i.e. a/c off it idles ~850, a/c on it idles at ~900).

I am sure someone will chime in and tell us how to check the ISV.

Good Luck!

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Nick Hromyak
'85 Carrera 7 & 9 Fuchs
Havin' Fun in Sacramento

Hello

I hope it was covered somwhere and has pictures.

1.) Check idle set switch on Throttle body
This unit should lift the ignition to 10° BTDC at idle.

2.) Check trottle body switch
Resistance should be 0 Ohm at idle postion

3.) Check for vacuum leaks

4.) Check the idle stabilizer unit
Remove it with the wire hooked up and turn ignition on. It should open 50%.

Early cars have a bypass adjusting screw on the Throttle body ( covered with a plastic cap ). You could set idle by jumping the idle stabilizer on the relay contact beside the ignition coil.

Grüsse