I've been working on my son's '87 924S in Northern CA and can't seem to get it to start and idle correctly.

It's hard to start (sometimes) and will only idle correctly for about 30 seconds before it starts to stall and die. I can sometimes feather the accelerator to get it into higher RPMs and sometimes it just stalls out. If I can get it above 3000 RPMs it seems to run fine. Anything below that and it seems to miss. Once it gets down to idle speed it will stall.

I've checked fuel pressure by jumping the relay and while it's running and it's dead on. It runs just as poorly with the relay jumpered. I've used Clarks Garage's method of checking the AFM and it's smooth and within spec. The temp sensors are within spec. I replaced the distributor cap and wires with the old set I replaced last year and there was no change.

I have not replaced the speed/reference senders, although they're within spec for resistance (I don't have an oscilloscope), nor have I replaced the O2 sensor.

Not sure where to go from here except to pull the intake and replace the Idle Control Valve and check the fuel injectors.

I tried to take it to East West Motors Porsche repair shop in Fairfield, but he told me he wouldn't touch the car because it was too old (thanks).

Any advice would be appreciated or if anyone knows of a NorCal shop willing to work on a 924S, let me know! Thanks.

 

throttle position sensor?

 

Good point. That caused me a problem with my 928 so I was made sure to check the TPS at the connector when I had the DME removed. It seems to be working correctly.

 

unplug the idle valve and see how it runs

 

It didn't run any better or worse when unplugged. I was thinking it might be stuck so I sprayed some carb cleaner down there and that didn't change anything either. I'm getting pretty frustrated with this problem.

 

Vacuum leak?

 

Are you sure the AFM connector is making good connection? My car ran like that when I forgot to plug it back in after replacing the intake gaskets. Also, the ref sensors might have the proper resistance but the gap might be incorrect or the ref sensor bracket loose.

 

That does sound like a vacuum leak. Pull the j boot and inspect it.

If it is surging at idle and wants to die, check the front temp sensor, sensor may be fine, but if the wiring is bad, it will do the same thing.

How does it act with the IAV unplugged?

 

I'd talk to the guys at Parts Heaven in Hayward and Easy Por in Emeryville. Bauer Porsche in Oakland might also be able to help.

 

that symptom sounds like a major vac leak - if you were to read the Porsche manual it would tell you how to pressurize the manifold assembly to find such leaks - follow those instructions carefully.

 

924S update - I pressurized the intake and hear a leak, but couldn't find it. Finally gave up and towed the car to Bauer Porsche repair in Oakland. They smoke tested it and found that one of the hoses off the idle air control valve was cracked and leaking. They had the car repaired and back in my hands the next day. Great guys and quite a collection of Porsches there for service. I highly recommend them based upon my experience.

 

Next time use a spray bottle with a few drops of dish soap to find the leak while doing the compression test.

 

Great idea. I tried that but the leak was buried under the intake manifold and I couldn't see it. I even tried spraying carb cleaner around to see if the idle changed with no luck.

 

Yeah, that's a toughy. I'm glad you got it all running again.

 

I had a friend listen to my 924S after my first try in starting it after the inital head rebuild due to PO losing a cam belt and bending some valves. I could get it to run above ~2k rpm but wouldn't idle worth a damn. He listened for about 10 seconds and said I had a vacuum leak. Sure enough under the intake manifold. Forgot to connect a hose. He had worked for Fairly Reliable Bob's auto dealership in Boise Idaho for a good while. That explained a lot.