Engine Vibration @ 1000 and 2000 RPM

[george996]

Hello everyone, I just joined and am looking forward to sharing information.

I have a 2004 996 Carrera 6sp with 20,000 miles, all stock. There is a slight engine vibration at 1000 rpm and a moderate vibration at 2000 rpm. The symptoms are the same whether in neutral, in gear, moving, stopped, load, no load, cold engine, warm engine, etc. There is also a rattling noise from the clutch area when stopping the engine, no rattling when stopping the engine with clutch depressed.

I saw a posting with similar symptoms on a Boxster involving exhaust system. I was able to eliminate about 70% of the vibration by loosening the long muffler fastening bolts.

I am wondering if I have a bad muffler or DMF or both. I test drove an 03 with tiptronic (no DMF) and noticed very slight vibrations at the rpms mentioned above. This makes me think the vibration is the muffler resonating.

I would appreciate any help on the vibration and rattling. Thank you.

P.S. since since I wrote the above posting, I replaced the mufflers with a set from a 2002 996 and still observe the same vibration.

Edited March 1, 2008 by george996

[porsche34]

As i can see you never received an answer regarding your engine vibration...,

Since 2 years now did you finally found the problem

Thanks

Robert

[15psi]

I had a similar problem on my car. Really irritated me. I recently pulled my engine/trans to replace te IMS, AOS, plugs, VarioCam pads/chains, and a bunch of seals and stuff. One last thing as I was reinstalling the muffler, I found a bracket was broken. I moved the clamp to solve the problem.

After I completed everything, I started the car and was happy to see the 'vibration' was gone. Not sure what exactly fixed the problem since I did so many things, but I suspect either the very very loose plug or the muffler bracket.

[george996]

As i can see you never received an answer regarding your engine vibration...,

Since 2 years now did you finally found the problem

Thanks

Robert

Robert,

It's a long story. I replaced alot of parts, o2 sensors, spark plugs, motor mounts, MAF, DMF, headers, stock mufflers, moded mufflers and cats. The only thing that made a noticble differnce was the set of used stock cats. The vibration is still there but almost nonexistant. The headers and mufflers changed the haracteristics of the vibration but i didn't like the loss in low end power when these were installed. With 997 headers the vibration at 1000 is completely gone and minimal at 2000rpm.

I drove other 2002-2004 996's, 6sp and tiptronic, some were silky smooth and others had similar vibration but less. I performed a leak-down test, everything was good. My next step to replace the cats with AWE or Cargraphic 200 cell versions but I am holding off since it is tolerable at the moment. I also own Durametric software and all vitals are good. I also narrowed it down to cylinder bank no. 2 by installing extra u-bolt restraints. I took the u-bolts off and would like to solve the root cause instead. Also, cylinder bank no. 2 has a small valve stem oil leak in one of the exhaust valves and I wonder if this has something to do with it, fouling/clogging the cat. However, all vitals are good such as cat efficiency, down stream o2, etc. Oil consumption is much less than the allowable so I don't think this it either.

Any comments woud be appreciated.

George

Edited June 23, 2010 by george996