chris_in_nh

hi, i've posted this message on ppbb and renntech as well, but haven't really heard any 'expert' opinions, so figured i would try here. here's what happened...

i was driving home tonight and all of a sudden, i got this stuttering vibration like i was driving over rough pavement. i instantly thought that i had a flat tire, and let the wheel loose in my hand to see if the car would pull hard to the left or right, but it didn't. tires are fine.

i was able to make it home ok, but was very nervous. i just hit 100K miles a little while ago, so engine failure has been a concern at this point.

the car is a 97, manual, 103,400 miles. has been driving fine, no problems at all lately. the vibration just started out of nowhere as i was on the highway in 5th gear doing about 65-70mph. when i pressed the accelerator pedal, i got a lugging kind of sound/feeling/vibration. i still had power to accelerate, and the vibration didn't seem to increase with rpms. the vibration was not an 'in the washer machine on the spin cycle'-type, violent vibration - it was kind of 'soft' like lugging, but very noticeable.

i noticed that when i took the car out of gear (i.e. pressed the clutch pedal) the vibration stopped. when rev matching to the next lowest gear there was no vibration. if i then coasted in that lower gear, no vibration. but when i stepped on the gas in any gear, i get the vibration.

the clutch seemed normal as it always does. no change from the usual. no clunking when changing gears, shifts smoothly, pedal travel/feel normal, etc.

i also did not get a CEL, which i was entirely expecting. at least a CEL would give me a clue!

i am thinking it could be all kinds of things. any expert advice, or has anyone had a similar experience?

i know what out-of-balance wheels feel like, and i am sure that it is not the problem.

thanks.

Jay Laifman

Well, I can give one thought: catastrophic motor mount failure? I only offer this from your description, but not from any knowledge of this happening in Boxsters before or from knowledge that a failure of a motor mount can do this to a Boxster.

LUME1

I would think this is the best place so start. If it was tires, wheels bearing, brakes, CV joints all the way up to about 1/2 through the trans it would must likely be able to be correlated to vehicle speed, ie increasing or decreasing frequency. Try reving the engine in the driveway. If the vibration is there you have just eliminated all of the rotating parts after the trans. At that point inspect the mounts.

If the car needs to be moving then you should start looking after the trans. I would look for leaking CV boots (bad joint), however this is usually a constant vibration, wheel bearings, jack the car up, grab the top of the tire and see if there is any movement.

After that give the result and maybe I, or some one else, can help more.