I have a 1990 C4 Cab 964 3.6 L with lightweight flywheel

When I got it, I had serious problems with the car just dying on me randomly while idling.

I have done the following.

1. Replaced both coils
2. Full tune up with new spark plugs (Top and bottom)
3. New Distributor rotors
4. Changed the chip in the computer to Steve Wong chip for LWF

After doing all of this I had the same problem. I then replaced the ISV. The problem has stopped. The car no longer dies on idling. BUT!!!!!
It hunts for idle. When Im in stop and go traffic. I lurge in first gear and push clutch and release the car out of gear. The RPM's drop to 200, then 1400, and then in a 1.5 seconds settle at 800 RPM's.

I have pulled the throttle cable and the microswitch does click as soon as throttle cable is engaged.

As a side note, which may help....On strong acceleration the car hesitates for a microsecond without change in the RPM's

WHAT NEXT?? O2 sensor???

Thanks,
Raghu

 

Maybe a vacuum leak somewhere?

 

How do I diagnose that?

 

I hate to say it, but I've had one that was just impossible to resolve and another that was as solid as a rock. Even swapped components between cars, no avail. It's a crapshoot.

 

Checked your oxygen sensor? Relatively cheap to replace and they do wear out.

 

I had the exact same symptoms, a new O2 sensor cured the problem.

 

A Bosch Hammer or Doug Boyce's Windows based scantool. You need to look at the actual values from the various sensors. Otherwise you could be replacing parts $$$ until nothing original is left.

 

I dont have the LWF, but have had idle problems. I found the following thread usefull. I'll take the car for a good drive this weekend to see if my work has paid off. If it doesnt it'll be going on the Bosch Hammer for the adaptation.

Chris

http://forums.pelicanparts.com/porsc...-gremlins.html

 

O2 sensor would be an easy try. Failing that it could be a vacuum leak which means checking all the joints etc. not easy.

 

Also, check your ground cable from chassis to engine/transmission. My brother´s -90 C4 had some idling issues, cured by renewing bad ground cable.

 

Do you have to remove the alternator / fan housing to access this?

Thanks
Chris

 

Sorry, should have been more precise. Transmission ground strap is a correct term for what I mean, it´s under the car. Pelican Parts number is 999-611-920-20-M260.

 

Raghu,

I've been having some idle issues which have recently remedied after I discovered a leaky hose on my crank case breather. After tightening the clip on the hose the issues have all but gone. I only realized I had a leak when I developed an oil leak as a result of filling my oil reservoir up otherwise it would not have been apparent.

Dave

 

Also worth having a look at the connections of the main battery earth strap, especially the end that attached to the body. They can corrode badly and start to cause all sorts of miscellaneous problems so cleaning it up is a quick and easy job that's well worth doing anyway.

 

x2 what Jim Howley said ^