Walt

Yes, have gone thru the archives on this. I've had a 1982 SC for 20 years but this Porsche is very new to me, its a 1981 with a 1991 3.6 transplant. Have not had this car long but have been experiencing some issues including oscillating idle and a rapidly falling idle at shift resulting in a stall at times; this occurs always from cold and sometimes warm. I also hear a slight backfire on occasion.

The car has a LWF, custom header, dynomax muffler, a cone air filter and a "reprogrammed" cyntex chip from 2004.

I’ve checked all the basics including O2 sensor, ISV, MAF, throttle position switch, CHT sensor, DME relay and distributor belt. I found the O2 sensor disconnected and it appeared to have a poor ground. A new sensor improved the situation but did not cure it.

Not sure what else to look at maybe a vacuum leak? Went around the intake runners with some propane but couldn't hear much change in idle but also couldn't tell when directly injected into air filter. The chip is 15 years old and I am sure lots of upgrades have been made in that time but hesitant to pull the plug on it until everything else has been eliminated.

Thanks, Walt

aldo964

Coils?

Walt

I detected a small gas leak around #3 intake stack. Will try and pull it this weekend, maybe a vacuum leak there.

Trapperbay

Fuel pressure regulator?

lateforlunch

how about system adaption? has it been run with the hammer or system 2 tester?

euge

Just went through the dance...
Places to check:
1. AFM, make sure connection is good in the connector - Do you experience hesitation when pressing the gas pedal quickly? If so, then AFM for sure.
2. ICV and hose that comes out of ICV facing you. Because of age it may collapse when idling. I had to put a spring inside of it to prevent that from happening. ICVs are about $70 from Germany on eabay, brand Lowe or something like that. Works great, easy replacement, 3 bolts.
3. Dirty Air filter
4. Vacuum leak somewhere

Navaros911

Good advice already, but I'm adding checking the air fuel mixture at idle and adjusting. This is done by a hex screw hidden in a hole of the AFM. With the AFM mounted the hole is at the left back of the engine bay (toward front of car). You won't see it, but you can feel it. It is normally plugged, but somebody may have removed it in the past. Counter clock wise is leaning out and clock wise obviously causes richer running. Doing some trial and error may work, but keep track of your turns and reset to your starting point if things don't improve.

Running rich may cause rough running and stalling when at idle and no issues while driving along... since the latter is controlled by the DME.

Walt

This is a 3.6 conversion with an AFM not an MAF so no adjustment available at that location. Sorry, I see my original post indicating MAF was incorrect. I will need to research CO adjustment further on this setup.

JasonAndreas

The Cyntex chips (I have several of them) did absolutely nothing to fix the LWF idle problem. Do you have access to a stock chip? If so, put it back in before you do anything further. Or buy the latest Steve Wong chip. Does the ISV valve rotate freely if you shake it? If not, clean it but don't use brake cleaner on it! Don't bother taking it apart to adjust its starting position either, you'll just cause more problems for yourself if you ever have to pass an emissions test at idle.


Do you have a MAF or an AFM?


Is it a backfire or a gurgle? If the overrun fuel cutoff is disabled to help with LWF stall problem then you will get extra fuel in the exhaust but its more of gurgle. A leaking joint on the exhaust side can also cause that. With the engine running at idle, you can very temporarily block the exhaust outlet to help pinpoint it.

Walt

Jason, I don't have the original chip and am leaning towards replacing the Cyntex. It is an AFM and it is more of a backfire than a gurgle. The ISV checked fine. Thanks,

tonymission

My first thought once I saw he had LWF was to get a Steve Wong chip. Fixed my idle issues assuming he doesn't have other things going wrong.