About Charles Griffiths Expertise Porsche Air Conditioning
Experience Extensive research in Porsche air conditioning problems, and development of upgrades and updates.
And experience in Porsche power steering system remanufacturing.
Organizations Porsche Clubs of North America.
Mobile Air Conditioning Society.
Publications Rennlist Forums.
Pelican Parts Forums.
And see hyperlink below:
http://www.griffiths.com/achelp/index.html
Expert: Charles Griffiths Date: 2/23/2008 Subject: Porsche 944 erratic idle
Question I've got a 1986 Porsche 944 NA, 5 speed, that will occassionaly start idling at around 1600 rpm, and then immediately back to around 900 rpm, and then right back to 1600 and back to 900 and on and on... Actually, it has turned into the norm, where it now only occassionaly idles correctly at 900 rpm or so and the majority of time is doing the 900-1600 idle "dance"---a real pain. I've checked all hoses and they all look to be good, and the fact that it will occassionaly go back to the correct idle leads me to believe that it could possibly be the 'idle control valve" that is the culprit, not a vacuum problem at all. However, is there a way of checking this out prior to just buying a new ICV and installing it? $200 and about 5 minutes replacement time would be CHEAP at this point if it IS the problem, but I'd rather test first, rather than just replacing and hoping, know what I mean? This has been a well maintained vehicle, so things like spark plugs, wires, etc. are all in good shape, so can I test the ICV for proper operation and/or are there also other items I should test as well that could be causing this idle fluctuation? Thanks!!
Answer From many posts on the net:
To test the ISV.
There is a Test Plug located near the Fuse/Relay box.
Engine warm. You jump pins B & C.
Adjust the idle with largest screw on Throttle Body.
Remove jumper.
Take a short drive and see if problem is resolved.
There is a procedure to attempt to clean the ISV as well.
Otherwise its most likely a vacuum leak and there are plenty
of sources or points to check, especially where a hose connects
to a component the end of the hose tends to harden if not break
in time on a 22 year old car.
If you can find someone with a "smoke machine" you can find
leaks quickly.
If you can't find component schematics for the 944 I on the net
I would search for a used Shop Manual which will save loads of time
in trouble shooting.
