Help 3.6L Conversion - Idle Problems

[jasoncrow]

I have a 1974 911 with a 1995 3.6L Conversion, which includes a 1995 DME and a flywheel and clutch package from Patrick Motorsports. When I bought the car I immediately noticed that it had a horrible cold start, it usually takes 2 - 3 mins of coaxing before the idle smooths out and the car will run without stalling. Once the car is warmed up the idle sets in at around 900 rpms and runs great. After investigating we found that the idle control motor was missing. We put the idle control motor on and the cold start problem went away. The problem we were left with is that the idle started at 1100 rpms and then crept up more and more, it never dropped back down, it's idling way too high.

[tholyoak]

Do you have a restrictor in the breather line from the intake boot to the oil tank. If not you will get too much air and the car will also die when you remove the oil tank cap to check the oil level. Also look for intake leaks at the rubber connecting pieces between the intake manifold and the short stub pieces that bolt to the heads

Todd

[Embs]

Make sure your TPS is plugged in, mine was left unplugged and it did this exact thing.


Thoalyoak, thanks for your DME electrical help a while back, I really appreciated it .

Todd Embs

[Joe Bob]

Air leaks are one culprit.....also the microswitch on the throttle linkage needs to be engaged to activate the idle circuit. I had BOTH issues....damn thing sounded like it had a lumpy cam until I corrected it.

The microswitch NEEDS to have contact with the throttle arm to work right when at idle.

[Kevin Stewart]

make sure the throttle cable isnt to tight, Kevin

[jasoncrow]

The car runs fine, without the idle control motor, I just have to give it gas while the car is cold. With the idle control motor installed I got an 1100 rpm during the cold point and once the car warmed up and switches programs to the regular idle, the idle goes up to 2000 rpms. If I disconnect the idle control motor after the car is warmed up the idle drops back to 900 rpm and runs normally.

[tholyoak]

Embs

Glad I could help out, many on this board have helped me a great deal in the past.

Well if your car will idle without the idle control motor then you definately have a large intake leak. Disconnecting the idle control motor the car should die immediately as with the throttle at idle the butterfly valve in the throttle body is completly closed so an intake leak after the throttle body must be present, or as suggested above your throttle isn't fully closing and is hanging up on the throttle cable

Todd

[pbs911]

IO had the same problem and it was the throttle cable. I added a PMS throttle cable and extra return spring at the throttle body which did the trick.