Question: I have a 05 R53....scanner shows a Knock Sensor code (no service engine light is on).
I started to get a vibration when I accelerate that got pretty bad. I found the lower control arm had one bolt missing and the other was backing out. Fixed that, and torqued them down.
Car was fine for a drive or two, then the shake started to come back, little at first, then pretty significant. Popped the hood, and found the right side motor mount bolt to be working itself out.
So I made sure all the mounts were good and snugged, but the car still has a bad vibration ONLY when accelerating.
Could this be the CV joint?.....I did see the passenger side boot is ripped, but I can't recall hearing any clicking noises when turning. There a sure-fire way to tell if the bearings in the joint are shot (like grab it and it shouldn't move kinda thing)

Just looking for things to help pinpoint the issue....I do have a new knock sensor as well..

 

Yes, quite likely a drive-shaft. If you grab it there may be a tiny bit of in&out movement, but none at all up&down.

 

You should check the passenger side motor mount, not the bolt holding it. If it's compressed all the way or leaking fluid, it's bad.

 

I think the passenger side looks ok......

 

TSW mount?

 

It was on the car when I got it quite a few years ago, but it is a TSW mount.

 

If a CV boot is ripped there's the risk the bearing has been contaminated with dirt and this will ruin a bearing in no time.

I had another brand of car that manifested ripped boots due to age/exposure. Tech removed the axles and cleaned the bearings and gave them a careful inspection. He deemed the bearings reusable and I went with his recommendation. New grease. New boots. Like new axles. Put over 50K miles on them after (they had about 250K miles on them when the boots failed) and the axles/bearings were fine.

Just mentioning this that while the failed boot may not probably does not account for the vibration you shouldn't drive with the boot torn. In the case of the car I mentioned above new factory axles were (this some 5 or 6 years ago) nearly $1000/each.

 

The stock motor mount is hydraulic and helps eliminate vibration. Your older TSW mount is urethane and transmits vibration. Given that your passenger-side mount is urethane, its likely that your lower motor mount is also solid and would contribute to the vibration. Another thing to check: if your rims have curb rash it's quite easy for the rims to be out of round and not balanceable. That would also cause vibration. Tip: Cardone sells rebuilt axles that are substantially less expensive than OEM. I've had them on my MC40 for years with no issues.