Cis problem

I hope there is someone out there that may help with this one. At idle after start up when the car idles down, the idle is 1000 rpm. After full warm up (the needle pointing near horizontal on the temp guage), and you come to a stop out of gear the idle is at 1800 rpm. If the car is left in gear and the idle is brought down forceably below 1800 rpm the car idles at 1100 with out problems. Everything else seems fine. I think it sounds like a CIS problem. Any ideas where to start or should I take the car an hour each way to the porsche mechanic?
thanks matt

Try disconnecting the small vacuum line (and plug the line) on the de-acceleration valve (4" diameter, 1" thick, metal component with one small line on one side and two large lines on the other).

my 82 did the same thing, i disconnected and plugged the vacume line from the de-accel valve and solved the problem.

I doubt it is this, but it may be worth getting someone to press the accelerator pedal down and up and for you to observe the movement of linkage.

Slight sticking of the throttle linkage can produce strange symptoms that can incorrectly (and expensively) diagnosed as fuel injection/ignition problems.

Just a thought,

- roGER