User 121721

Make sure that this isn't the normal "shaking" that all 993s seem to have, mine included. Initially I thought there was something wrong but the dealer told me that "they all do that," which was subsequently confirmed by Robin Sun the first time he saw my car.

I'd love it if these cars idled as smoothly as a BMW inline 6 but they simply don't. I don't know why that is, but it is what it is. There have been many threads over the years about the rough idle that everyone notices, with many people adjusting their ISV to a higher RPM to smooth things out a bit without having to run the AC all the time.

CalvinC4S

Sounds like a harmonic imbalance caused by Dual mass fly wheel. By hitting the A/C it changes the harmonics. If you have ever played a string instrument, sometimes a certain note from a out side source can cause a string to start to vibrate even though it wasn't touched.

I have no smart way to describe what is happening other then that.

Wiki is better at it. http://en.wikipedia.org/wiki/Resonance

Monique

Check ISV then vacuum air leak.

GL

mc_opp

Thanks for all your suggestions. My mechanic is very slow, so that it may take a while. I will follow up on each of your comments. Hopefully, one works out!!! Just a last question. Is it possible to swap out the ECU with a different 993 and see whether the ECU is causing it?

Augustus Davies

Rob at SCARGO most likely swapped out the ECU when he trouble shot your car..

ard

Based on your original post it sounded like you were "done" with taking the car to shops (understandable), but based on your current post it seems you are having these issues looked at by a shop anyway? Just trying to confirm my understanding.

I believe we talked in person a few weeks back, and although you may be reluctant to take it to yet another shop I would reiterate my recommendation to take it to RMG in Sunnyvale. More than the average number of "head-scratcher" cases in the Bay Area end up there, so at least Bob Grigsby may be able to tell you whether he has seen the exact same symptoms. I have used RMG and it is my impression that few if any unsolved cases leave his shop in the same unsolved state.

Just my $0.02

Best of luck getting this sorted out.

By the way - do you have any paperwork predating your ownership of the car, to see what work has been done on the car? Perhaps you can go to a dealer and ask them to look up their records on the car, on the off-chance that it was serviced at a dealer post-warranty. Are you able to contact the previous owner(s?) to at least find out where the car was serviced and what was done to it?

Don't lift

I had the EXACT same problem and it went away after a clutch job including replacing the DMF........
Thanks to Chris and Robin !

Also, I kinda remember the shaking got much better if the clutch was depressed.......try engaging the clutch and see if it makes any difference. Good luck!
_____________
'97 blk/blk C2S

mc_opp

Hi,

Thanks so much for all of your comments. The problem has become less pronounced after making the following changes(i.e. the engine runs much smoother)

- DME relay replaced
- Alternator and fan belt replaced by genuine PORSCHE
- another check of rubber manifold (vacuum leak): none detected
- check distributor belt (seems fine)

However, the issue is still there. I will now replace the dual mass flywheel. Since you have to take the engine out anyway I will also do a clutch job. I want to go for the OEM replacements, i.e.

DMF 964 114 012 02
Clutch Kit: 993-116-911-01

given my problems this seems to be the right choice. Comments appreciated!!

geolab

hello,
I would suggest two things to change before taking engine out. If this won't resolve the problem, I will buy the parts back from you.

1st change the throttle valve switch part number 944.606.116.01 or bosch equivalent 0280122004
make sure you source the part from reputable shop, because there is a lot of chinese copies out there.
this part mounts on the throttle valves.

if no luck, 2nd change ignition switch part number 993.602.706.00 or bosch equiv. 0227100200
also from a good source
this is under driver seat accessed from the back. get some computer thermal paste to apply between this part and the aluminum radiator plaque it mounts on.

If this doesn't solve the problem, I will buy both parts from you
If it does solve the problem, donate the check, regards

mc_opp

Isn't the throttle valve switch number you gave me the one for the 944?

Thanks for your comments. I will try it out.

TheOtherEric

I like these suggestions. I would doubt it's a flywheel problem since the problem only happens once warm. Just my 2c.

1pcarnut

When I got my 993 it seemed like it didn't pull as strongly as it should. Turns out the varioram was not actuating. There are four vacuum actuated valves that are on the motor and the rubber diaphragm fails with heat and age. They had all failed. There are four of them if I recall, one on each side of the intake manifold (on top), one under the manifold and one just about the dizzys. The updated version looks to use a silicon based diaphragm that might last longer. HTH

vjd3

My 97 shook a little at idle, was smoother with the AC on. It did it before I replaced the clutch and flywheel with the LWF parts (and did the top end on the motor). It still does it now.

My preferred mechanic said swapping the ECU with a TechArt one (or other modified version) can take care of it, as well as wake the car up a little powerwise, but it's otherwise just a characteristic of certain 993s.

JM993

No offense to you, but that sounds like a lazy mechanic.

vjd3

No, he's an experienced one, and has seen it before on numerous cars.