1998C2S

Hello all,

Just thought I'd take a moment to introduce myself to the forum. For a couple months now I have been a reader, but am now a poster since I am the proud new owner of a 1998 C2S, black on black, with turbo S spoilers f&r. Love the car so far, but a couple issue have arisen, so bare with me, since I am not nearly as knowledgable as all of you. My honest feeling is that every car with 50K miles has a few stories to tell, but figuring out what they are is the hard part, right?

The car runs strong, but the perceived problem happens at idle speed. Once the car has warmed up a bit, and sits at idle, the idle speed drops to about 500 (lower than normal according to friend). Once this happens, it kind of bounces around a bit due to the low idle speed. The concerning part is that a periodic clunking sound from the front of the motor becomes apparent as it bounces around 500 rpm. It can be best heard when one sticks their head around the front of the rear tire. Could it be a belly pan, or heat shielding under the car, or what?? The clunking sound is not noticable at slightly higher rpm, so is the fix as easy as upping the idle speed??

I am confident in all your knowledge, so any advice is greatly appreciated. I am sure that once all the questions from me are out of the way, I will also be able to adivse newbies like me.

Ciao,
Bryan
Delray Beach, Florida

PS - had a 996 for a couple years, and now I know what you all figured out already - the 993 is the best Porsche ever

And don't worry, many more newbie questions to follow!

Howdy993

No expert here, but you may want to get a new Idle Stabilization Valve (ISV) to keep the bouncing around at bay.

Welcome and Best wishes!

Wreck Me Otter

Do a quick search of "ISV" for instructions on now to clean it. If that doesn't see if you need to look further or replace it as Howard posted.

InTheAir

....or go here: http://p-car.com/diy/isv/

Flying Finn

First of all, welcome and congrats! 1998 C2S is one of the top 993s.

My vote for ISV also. Very easy, good first DIY project for you & your new baby.

P.S. Since you're pretty close, check out Regional Forum and our monthly SBBC (South Beach Breakfast Club), Key Largo drive etc. where us South Floridians meet every now and then. Come and join!

Terry Adams

If it's not the erratic idle due to the ISV, then the noise at idle could be that the PO fitted a LWF (Light Weight Flywheel). See if you can find someone local with a LWf to compare sounds at idle.

Wreck Me Otter

If the noise goes away when you press the clutch pedal, there's a good chance that it is a LWFW as Terry posted.

trojanman

Maybe it's just semantics, but my LWF has more of a "rattle" (I've heard someone describe it as "rocks in a blender"), as opposed to a "clunk".

Rough idle will definitely tend to accentuate any noise and I agree that removing and cleaning the ISV is a good first step... but anyone who says it is "easy" is a lot more patient than I am!! I had a hell of a time getting that thing outta there!

Good luck.

Monique

If you have a LWF, try increasing the idle to nearly 1000. It is 960 on the RS... is more because the alternator/fan pulley is smaller and there is less electrical output.

Nonetheless, there is a good reason for the idle rpm being higher.

Welcome to RL

c993k

Welcome Bryan,
It's good to have another C2S in South Florida.
Local PCA Club is very active. It's the Gold Coast Region. Visit the website
at http://www.goldcoastregion.org and get the latest things going on.
The rest of us have informal meetings and they are announced on here and on the regional forums.
The best investment you can make would be becoming a Rennlist member
By far the best place to get all your information
from the most knowledgeable 993 fanatics in the World!
Chris

lowblow

Welcome to the South Florida Frey.....Hey Finn, when is the next SBBC?

Mike

chris walrod

Possibly a failed dual mass flywheel? Have you seen any check engine light events?

Welcome to Rennlist! Glad to have another around!!

You already broke a few rules, where are the pictures!!!!

Scott 1996 993c2

Welcome to this place . . . your car sounds nice . . . but we do need some pics.

Scott

1998C2S

WOW, that is a lot of good info. Chris, no check engine light, so I would probably rule ot the dual mass flywheel thing. But, I think i will try the idle stabilitzation valve as soon as possible. It would seem that this idling issue doesn't surprise anyone, so i am comforted in that. I will feel better when I don't hear that crazy noise.

I guess I broke a rule by not posting pics, so sorry for that! I wasn't as prepared for my first post as I thought. Believe me, many pics will follow one day soon.

Again, many thanks for all the feedback on the issue at hand. Very busy at work, but i will hope to get out to a gathering or two, thanks for the invites. I look forward to swapping info, and getting with the whole air cooled thang!

Bryan

1998C2S

Many thanks to all who replied with possible solutions. I only wish it was the ISV like so many mentioned. That was an easy fix, even for a novice like me. Went to the local shop, and the news was not so good - tell me what you think of this: The clunking noise from underneath the car is likely due to the dual mass flywheel separating, actually becoming dual masses in the housing and bouncing around a bit. The low 500 rpm idle is due to the fact that the engine management reads from the flywheel, so the readings are incorrect due to that wobble within.

Suggested fix at this point is a new flywheel (and they are recommending another dual mass, not lightweight). Does this make good sense?? Also, am I wise to do the clutch while in there, since there is no additional labor charge for that. If all these seems correct, any advice on which flywheel and clutch to go with, and where to purchase.

Thanks again for the advice,
Bryan