Strange occasional vibration at acceleration
I have a 2001 330xi (98k miles) and it starts vibrating all of a sudden without any notice while I am driving and it will go away after some time (5 -15 minutes) automatically. It shudders only when I press the gas paddle. When it happens it happens even at lower speed but the intensity of the vibration depends on how much I my pressing the gas paddle. Some times the shudder is very intense (feels like I am driving with a flat tire) and sometime it will be mild. If I am not pressing the gas paddle there is no vibration at all.
The car will run fine for 2/3 days then all of a sudden the shudder starts while I am driving. Recently I am experiencing this problem more frequently.
I took it to the dealer twice and had one of the mechanics drive the car for half an hour on both occasions but unfortunately the car ran smoothly the whole time so we couldnít recreate the problem.
I have brand new 4 tires and they are all balanced. Initially I thought it's a tire issue (balance or air pressure) but after few weeks I am certain it's not a tire problem since it does not happen all the time. It's not spark plugs since the car is very smooth at idle and again it does not happen all the time.
Is it some kind of sensor problem that is sending wrong measurements?
Any help would be greatly appreciated.