[coriolis14]

Hey all -

I'm going kind of crazy trying to figure out a why my car (E92; N51; GM A/T; 118k miles; 100% stock w/ no mods) has a very strong, intermittent vibration that happens when the car is stopped. I've tried putting the car in Park, Reverse, and Neutral to see if the problem would go away, but I still get strong intermittent vibrations when the car is stopped. I do notice that the vibrations are slightly less strong in Park or Neutral as opposed to when I'm in Reverse or Drive. Going into M/S (sport mode) doesn't stop the vibrations either. This would seem to suggest the issue isn't transmission related, but I'm not 100% sure.

The vibration doesn't happen at all when the car is in motion: accelerating (even WOT), cruising at highway speeds and braking/slowing are still very smooth with no issues.

I've also used the Carly OBD reader to see if there are any faults in the DME, but the readout is clean (no problems).

A few questions for the group:

1. After doing a lot of research, I think the issue might be my motor mounts. I've never changed them or the transmission mounts. My employer recently moved to a new building that has a lot of sharp speed bumps in the parking garage where I work so it would sort of make sense that this problem would get worse if i constantly was hitting these things every workday. Would motor mounts cause the problem I described above?

2. Another suggestion was the A/T transmission was going bad. I'm not sure if this is the issue - I've changed the transmission fluid (drain/refill) and it still shifts very smoothly without any issues even at low speeds and when its cold. Would the A/T suddenly start failing this and act this way?

3. The third option I've looked into is a vacuum leak somewhere. Would the DME pick up on a vacuum leak if there was one or is the only way to properly diagnose a leak a smoke test at a shop?

4. The final option is a spark plug or coil pack going bad. I changed the plugs at 85k (33k miles on the new plugs) and the coil packs have been changed individually when needed. I feel like if this was the problem, the car would throw a CEL / wouldn't run smoothly when accelerating. Also I think the DME would know if there was a misfire or a weak coil pack though and would show it in an OBD scan. Let me know if that's not right though.

I'm trying not to throw time/money at the wrong parts or fixes so I appreciate any input - thanks all!

[coriolis14]

Update: I replaced the motor mounts, but the shaking is still there. No codes. My guess is the transmission is going bad - if anyone has any advice or input, I would appreciate it!