Vibration under acceleration
 

2000 Boxster S with 90K. There is some vibration with acceleration that drops off as soon as you let off the power. Revving in neutral is smooth. No vibration when coasting. My local mechanic, not a Porsche expert, was thinking it may be the CV joints but there is no clicking or other noise. Any thoughts?

Motor mount.

Front one most likely.

I would change the 3 of them

The front mount was changed recently. I don't think the others were, but I'll check.

IMS?

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Where do you feel it? Steering wheel? Braking? Seat of your pants? Could be lots of things until you narrow it down a bit.

My best guess is that it's a bad coil. I had a GM product that did what you describe. turned out to be a bad plug wire.

It feels like it's coming from the rear. Steering wheel does not shake. No shaking while braking. It feels like a tire or suspension vibration, but only when it's pulling under power. Let off the gas and it stops. Rev the engine while in neutral and there is no vibration. Just when accelerating, or pulling up a hill.

Check your wheel bearings.

Agreed, check you rear CV boots, wheel bearings with the wheels in the air, check wear on tires, get them checked for balance as well. Good luck

Update: Finally got it back in the shop. Left rear bearing was worn, but the vibration continued until both CV joints/axles were replaced. Also had a torn ball joint boot, and needed alignment. Now it runs great.