I'm hoping someone has had this problem before, or has some insight on it. Anyway, i have a 98 M3 sedan with A/T. I have had the car since Oct of last year and haven't had any problems until a few weeks back. About a month ago the car upon start had this heavy vibrating, kinda like what an aftermarket stiff motor mount feels like. It is heavy enough to feel and i can see the rearview mirror shaking pretty good. It does not affect performance at all, and goes away after 10 sec-1 min.
Now here are some things i can only throw out there (grabbing straws). When this first started i filled the car with 87 oct gas a month ago and added octane booster (bad gas shortage here in the Panhandle of FL then). It did it a fews times after that and then hasn't raised its ugly head until today. Been running straight 93 oct since I put in 87 oct. Only other thing I can think is I was low on gas this morning and filled up (right before warning light came on), filled with 93, drove about 10 miles and then it did the vibrate thing a couple times. One time it lasted about a couple minutes. Oh yeah, it does it at idle or moving.
My car has 87,500+ miles on it and besides this problem has been running great.
So, could it have anything to do with the 87 oct a while back, or the tank being basically on a couple gallons and maybe sucking up some particles causing a temporary issue? Sounds far-fetched to me, but I don't have a clue as to what could be causing this.
Thanks for your time...and if anyone has a clue please share!