TheOtherEric

by the way, if you decide to swap that part, I can mail you a used one to try out. You'll still need some thermal paste (it normally comes when you buy the part, but you can get it elsewhere).

I'm in the middle of a move so it would be several days before i could mail it, though.

KTM

I believe the ignition switch part is only for 1995, in latter years this was incorporated into the ECU so is not used. I agree with some other comments that this is roughness is a characteristic of some of these cars, although it seems like the earlier models are more prone to it, and the problem here is a 1998 model with the "better" ECU. I threw a lot of parts at trying to solve this problem, including a top end rebuild (needed it for the valve guides and SAI clean out at the time), clutch/flywheel, FI clean and balance, dist. rebuild, coils, ISV, MAF, O2 sensors.... list goes on.

Now things are better, but you still know the engine is running. I'll also throw out the recommendation for Bob at RMG, he has some thoughts on this issue, and can also give you an honest opinion if yours is within range of how other '98s idle. Also, do you notice any roughness at higher RPMs? If you put the Cruise on does the tach stay solid at RPM?

Good luck, keep us posted on your results.

geolab

hello, ignition switch is on all US and ROW model years, thnx

although the part number starts with 944 , it is the part number used as well on the 993, good luck

JM993

Perhaps it's just me, but the "some 993s just do this" excuse some are hearing from their mechanics is sounds like BS. I've been in lots of 993s early and late which do not exhibit this issue. In fact, my car idles every bit as smoothly as both of my other cars (both BMWs with inline 6s). Hate to be the bearer of bad news, but if it's not the DMF, I'm betting something was missed when the OP's car was checked by one of the several mechanics he visited (who it appears just threw parts - and the OP's $$$ - at the problem hoping for a fix). I'd suggest a retest of the vacuum system by checking to see if it holds pressure (it's an easy test documented in the factory manuals).

Best of luck.
Joe

chris walrod

While it is true that the 993 does typically have a rough idle (harmonic balancer gone on the 993), I feel that some of this is a result of cam timing that may have slipped out a tad. Most of the 993 rough idle problems we see are on the 96-98 cars.

C4S993

I once had a 1995 C2 Cab and the car shook and was undriveable for maybe 2 mins and then was fine. On and off this continued and one day, new clucth and flywheel and no more problems.

Patrick
1996 c4S

ClaesM

I changed the lamda unit after it car was uneven in idle mode. That worked.

cbush

My was missing and dying at idle when warm. Took it to the dealer who worked on it for two days, and finally "narrowed it down" to about $4000 in parts, but they really didn't know for sure. Took it to an independent, they replaced the plug wires, and it is fine now. I know you said you tested yours but if they are old, it would be something to consider.

mc_opp

According to my mechanic, the issue has been resolved. Apparently, the DME relay was the final component that made it run smoothly (which has not been installed the last time I drove it (although I thougt it was)). Unfortunately, I won't be able to pick up the car until next week (will keep you posted) and I am not sure whether he has driven the car long enough for the idle problem to become recognizable (one has to drive at least 20 minutes). I will post my verdict next week.

brucec59

I can't see how a DME relay, which merely supplies 12V to the DME (or not if it fails), can cause a rough idle. Good luck to you.

goofballdeluxe

Congrats! So, who gets the $100 reward you promised?

CalvinC4S

Chris, as it is the DMF

mc_opp

Hi, it drives much better now. It is hardly noticeable (but still a little bit). I was told before by quite a few mechanics "porsches just do this". THIS WAS COMPLETE BS.

Now the car has come down to an idle that is hardly noticeable (and not annoying). I believe that a combination of all of your recommendations made it better. However, I am really not sure whether I can push it further and do the last two things: throttle valve switch and change ignition switch part number. These seem low-cost to me and may solve the final 5% that are missing.

I also feel that the clutch (note there was not clutch job) now works much better. The car used to die on me in situations in which it was not my fault (I am from Germany and have been driving stick shift for the past 13 years :-)). It runs much smoother.

JM993

Bravo!

Body Roll

This is all the excuse I need to do a clutch and DMF replacement on mine.