Unstable Idle Issue
 

I have an '87 911 Carrera that normally runs perfect, but just recently it started having this unstable idle. It usually happens if I'm cruising with the rpm's above 3k or so and then I let off the throttle to come to a stop. The idle starts to drop like normal, but then sticks between 1200 and 1400 rpm's. After about 10 seconds of this high idle (not touching the throttle at any point) it will drop down to it's usual ~900 rpm's.

If I punch the throttle while it is idling high, it will rev up as expected and then fall to its normal engine speed (~900 rpm's).

Any ideas?

Binding throttle cable.

Have a look at the linkage where it connects to the transmission... I had to take mine apart and clean & lube the bushing because my throttle would hang as well !

Phil

When it is safe, pull over and pop the lid, take a butt of a screw driver and tap firmly on the ICV, if it settles down, you may need to pull the ICV and clean it. Search Threads.

To do a proper check, check the OHMs per Bentley.

sounds like a sticking throttle cable to me. I had a similar problem. start at the throttle body and work your way forward.
http://forums.pelicanparts.com/porsche-911-technical-forum/534845-hanging-idle-fixed.html

I'm with Wildcat077 on this one...the linkage on these cars usually seem to stick in the area where it attaches to the trans, as soon as the weather warms. Disassemble, clean, lube, reassemble.

Thanks for all the replies! I'll start with checking the linkage and lubricating along the way. I was thinking it could be the ICV/ISV as Draco said, so maybe I'll give that a clean too.

Simple. Just needed to lube the throttle linkage at the transmission. Thanks for all the help.