[bigxO]

I’ve been noticing a vibration in my 328i E90 (N51 engine) for a while, and it seems to be gradually worsening. The vibration is only present when the car is idling—whether I’m at a stoplight or in park—and it disappears as soon as I start driving or increase the RPMs.

I suspect it might be related to the motor mounts or transmission mount, but I haven’t done any inspections or diagnostics yet. What could be causing this, and what’s the best approach to identify and fix the issue?

[Phil325i]

If it's motor mounts, open the hood and watch the behavior of the engine when you blip the throttle. If the mounts are shot, the engine will rock side to side.

[bigxO]

I’ll give that a try and see if there’s any movement when I blip the throttle. If the engine does rock side to side, is there a specific way to check which mount (or mounts) might be the culprit? I might just end up replacing all the engine mounts and the transmission mount since I’ll already be in there, if that’s the issue. Also, any recommendations on replacement mounts? I want to make sure I get ones that will last or be better.

[Phil325i]

I'd always replace both engine mounts if I were you. I can recommend the transmission mounts from Rogue Engineering (at least for manual).

https://www.rogueengineering.com/Rog...air_p_137.html

[bigxO]

I tried stomping on the gas while holding the brake in D, but I didn’t notice any significant engine movement, so I’m not sure if it’s the motor mounts. The car has almost 140k miles, and I’m not sure if the mounts have ever been replaced since I just bought it recently. Is there anything else I should check to rule them out, or should I just go ahead and replace them given the mileage?

[Phil325i]

I think BMW mounts are pretty solid. I only replaced mine (at similar mileage to yours) as preventive maintenance when the sump gasket was changed.

[sabino56]

You might check the over running alternator pulley. Mine locked up and it caused a vibration at idle. When it’s idling and vibrating look at the tensioner - if it’s jumping that’s one sign that the OAP could be bad. There is a thread on this somewhere here if interested

[bigxO]

I’ll check the alternator pulley and tensioner for any jumping. One thing I forgot to mention is that the vibration starts around 700 RPM. Does that point more toward a mount issue or something like the pulley?

[sabino56]

I don’t think one could differentiate between motor mount problems or pulley problems based on rpm.

If motor mount has collapsed I think the engine mount support will be resting on the top bell shaped part of the motor mount. For it to cause a rattle at idle it would seem the engine would be vibrating on that metal to metal contact and would be kind of obvious. When I replaced my motor mounts, one was collapsed and I don’t recall any noise from it with engine running. I was just in there doing the oil pan and replaced them. You may be able to see if collapsed with a bore scope- I’ve never tried.

If pulley is bad, the rotating masses of engine and alternator vibrate with the belt as the spring. That would be rpm sensitive but no clue as to how to know what rpm. Here’s the link on my problem there https://www.e90post.com/forums/showthread.php?t=1962637

Good luck

[chris55552]

Originally Posted by bigxO

I’ve been noticing a vibration in my 328i E90 (N51 engine) for a while, and it seems to be gradually worsening. The vibration is only present when the car is idling—whether I’m at a stoplight or in park—and it disappears as soon as I start driving or increase the RPMs.

I suspect it might be related to the motor mounts or transmission mount, but I haven’t done any inspections or diagnostics yet. What could be causing this, and what’s the best approach to identify and fix the issue?

I would say combination of both your motor mounts and possibly your coils. Reason behind this theory is I just finished replacing my engine mounts and it made a huge difference, and just 3 days ago I replaced the stock coils with dinan ignition coils and the results were pretty noticeable. Engine feels much smoother now even at startup, no fluctuations just pure smoothness. I will say that I have also recently changed my vanos check valves and cleaned my solenoids, cleaned mass air flow sensor, new air filter and I also use an oil supplement by liqui moly called ceratec that makes the n52 run smoother and more responsive in my opinion. But I would say your motor mounts and if your coils are old, replace them soon as it makes a big difference.