Just picked up a '99 cabrio and i'm getting a pretty significant vibration throughout the whole car at idle. It stops immediately once I start moving but returns when i come to a stop. Being in/out of gear and having the clutch in/out have no effect on it, so at least I can rule a few things out. Any thoughts?

 

Maybe a batch tank of gas?

 

Maybe a bad tank of gas?

 

Interesting thought. It started halfway into my last fill-up though...

 

What octane do you use? When were the spark plugs (and other ignition items) last changed? How many miles?

 

I use 93 octane and the car's got 56k miles. I'll have to dig up service manual to check on the plugs/ignition, but I know the 60k miles major service hasn't been done yet so they may be a little old

 

You did not clearly state that it just started happening although you did state that you just picked up the car. So maybe you did not notice that it has done this all along. The reason I say this is that I just installed the RennSport motormounts in my car and because they are considerably stiffer they TRANSMIT the cam loping of the engine more directly so the feeling is that the engine is running rougher. It is not. The high performance mounts just send more feedback to the chassis. Check and see what COLOR DOT you have on the top of your motormounts and report back to the thread and I will post a followup. eric

 

Wish that was the case but it definitely has not been happening all along. I probably would have noticed during the test drive that the driver's seat felt like the chair in Sharper Image during idle...
I'll check the dots though and let you know. any other ideas?

 

Another possibility - You should check the battery and see if it's low.

If it is, then the alternator is pulling hard as it tries to run the electronics and charge the battery when at idle. This can assist in providing rough idle.

The Porsche battery maintainer solves that issue, always ensuring that your battery is topped up and ready to go.

 

People have noticed the passenger seat shaking (at the headrest) at idle on their 996s and mine included and have questioned it. So many on here have it that is probably normal.

 

Has the weather by any chance warmed up and if so could it be the A/C load?

I would change the plugs and all unless it's documented that they have been done.

 

I'm in New York so unfortunately the weather hasn't warmed up yet...
I'll play around with the AC/Heat, etc and see what happens. some new spark plugs couldn't hurt anyways. Any idea how much $$ a new set installed usually runs?

 

Just notice the same thing today....at ldel my passenger seat was vibrating, is that normal or is sometning loose?

 

Normal - but as I mentioned, I have seen a reduction in idle vibration after using the battery maintainer and keeping the battery topped up.

 

I don't feel much vibration in the driver seat at all. When I noticed that the passenger seat was vibrating, I thought for sure something is loose?
Strange.
Battery seems fine.