Vibration when accelerating

[USMC9953]

Hello all!

 

I've got a 1999 996 Carrera that hasn't had any mechanical issues outside of a water pump replacement earlier this year. Just today I noticed that when in 3rd to 5th gear (I haven't had it on freeways to see if it's in 6th too, but most likely it does) in the mid rpm ranges (2500 - 3000+) there is a vibration that I can feel through the gas pedal and throughout the car. When the gas is let up and/or when the vehicle is coasting the vibration goes away. The vibration seems to only occur on acceleration and does seem to be coming from the rear. The check engine light came on as well, at first it was flashing and is now constant.

 

Any tips on what this could be? Drive shaft? Engine mount? Catalytic converter?  .....?

 

 

[Bilal.utah]

Engine mounts most likely, i have the same thing going on, ive ordered a set of motor mounts so will see in a few days when they come, i get the same vibration even when parked and i hit the gas to about 3000rpm


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[Bilal.utah]

On the engine light flashing, it could be a failing spark plug or ignition coil, read the code to see which cylinder is misfiring, then change the plugs, if you want change all coils or just the one cylinder thats misfiring, mine did that but its excellent now


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[USMC9953]

Thanks! I'll start with the coils and plugs -- I wanted to do a good tune up anyway. I don't have a code reader (it's on my Christmas wish list) so I can't check to see what the alarm is...

[USMC9953]

So, I'm going to order coils as 3 and 5 are apparently misfiring. The question here is:  Are the left and right side coils the same, or is there a left and right side coil setup? Yes, to some this might be a dumb question, and it might be, but I don't want to order one part to learn I acquired the wrong side. Thanks!

[Uwon]

^^^^^ The PET in the Porsche Classic tab of the Porsche web site is your friend. Covers all years of the 996. The remarks column identifies particular years applicable.

http://www.porsche.com/all/media/pdf/originalparts/usa/996_USA_KATALOG.pdf

also, Pelican Parts for one will generally specify quantity required of each part.

you will probably need a few more items such as screws/bolts, heat shields, etc.

Take your time if you have it.

Good luck.

Johan

[Bilal.utah]

The coils on the left and right side are the same. Is one exhaust tip lower than the other ?


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[judgejon]

Consider investing in a Durametric code reader.

Good luck.  S F

[Bilal.utah]

Did you manage to fix you vibration? Mine still vibrates after changing the motor mounts


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[jabcas]

I'm also wondering if you got it resolved? Mine is vibrating like crazy when sitting still in neutral or driving. I can feel it everywhere in the car and on the car. There is a ton of vibration on the rear fenders and bumpers.  You can also feel it a lot in the clutch pedal especially when  you push it towards the floor about an inch. You can also feel the motor vibrating more than usual if you touch it. This vibration can be felt at any RPM and gets worse the higher it goes. There is a point between 3.5k and 4k RPM's where it's goes from bad to worse. When it's in that range or higher you can actually hear the vibration.   So far i've changed the motor mounts, trany mounts, IMS and Clutch. The shop said there was nothing  wrong with the flywheel and recommended not changing it. It vibrates regardless of temp. There are no check engine lights on. There are no other odd noises happening to make me fully believe it could be the flywheel.  The shop said the car did show some misfires and said maybe changing the plugs and coil packs could solve the vibration problem. Would plugs and coils actually cause that much of a vibration issue? It doesn't seem likely to me.

[DBJoe996]

Usually if it is plugs and/or coils it will start to throw misfire codes and the CEL will come on.  This sounds more like a bad DMF (dual mass flywheel)...or if it occurs when running at speed, the rear CV joints.

[jabcas]

1 hour ago, DBJoe996 said:

Usually if it is plugs and/or coils it will start to throw misfire codes and the CEL will come on.  This sounds more like a bad DMF (dual mass flywheel)...or if it occurs when running at speed, the rear CV joints.

I'm still stuck on thinking it's the DMF too. The only other 2 things I can think it could possibly be is the exhaust touching something it shouldn't be or maybe the harmonic balancer. I guess I will go ahead do the coils and plugs though anyway since the car's at 80k now.

[RFM]

Defective engine mounts can also cause annoying vibrations and noise, it is worth checking that too.