jumpinjimmy

Hi, I have a 911sc cabriolet with a problem of high idle when hot. The car starts easily, idles roughly at 900 rpms and then as I drive for a while it settles in to a 2000 rpm idle that won't go away. If I stop the car for a short period of time and restart, the idle once again stumbles at 900 and then starts to creep up to 2000.

From what I've read on forums, there seems to be so many different places to start troubleshooting...any suggestions? acccumulator? WUR? simply adjust idle and fuel mixture?? crack in airbox? vacuum leak??

Any pushes in the right direction would be appreciated. The car has a very complete service history and I see where the WUR was changed with a second hand unit at one time and then a new unit replaced that one a few years later. When I received the car, I also noticed one of the electric plugs to the WUR, the one towards the back of the car, had been disconnected. I reconnected it.

Thanks in advance.

Steve

jumpinjimmy

Did I not leave enough information or has no one experience with this problem?

TroyN

Have you checked/tested your idle valve (I forget if it's the AAR or AAV)? As you noted it could be anything though, all of the various pieces in CIS have to be working just so. See the thread "I need some help" for reference to a book that will help. You might be able to find some CIS troubleshooting steps on the web somewhere too. Eg:

http://jimsbasementworkshop.com/CIS/...IS%20Print.pdf
http://www.csupomona.edu/~bvnorum/ca...521-124-00.pdf

That second link looks to be maybe VW focused but the components are the same.

jumpinjimmy

That was really useful. Thank you. I actually gave the Auxiliary Air Regulator a tap with a screwdriver and it seemed to calm down a bit. It's still not running perfectly but I was encouraged.

jumpinjimmy

As I have just purchased this car, I have only know it has having this problem of high idle, so not sure if the idle was turned up on purpose. I decided to take the car and have the exhaust gas analysed and it was perfect. That being the case, I decided to just turn the knurled **** and lower the idle myself. Car running fine at speed, a little rough at idle at 900 rpms once well warmed up and pretty rough to start up. Not sure where I should go next.

Steve Weiner-Rennsport Systems

I would strongly recommend having the cold & hot fuel pressures (system and control) checked to make sure everything is in spec for cold starts, warm-up and normal running temps.

I would also check the intake system for any vacuum leaks as thats a big source for idle & rough running issues.

upier

Did you check to make sure the throttle isn't sticking?

jumpinjimmy

Throttle is not sticking and I think it's a good idea to have the line pressure tested. My problem is that I live out in the middle of nowhere in rural France and there's ins't a garage near here that I would trust to touch the car. There is one single garage that is a specialist in fuel injection and I've had the bosch injection on my old porsche 928 checked over there, so maybe I'll take it to him. I agree that the pressure is where I should start.

jumpinjimmy

I've also looked over the car for vacuum leaks and it seems to be in good shape. The intake manifold rubber looks relatively recent.