Vibration On Start Up & Idling
 

My recently purchased 2014 63 started randomly vibrating when both starting up and also idling at lights. Like it was an engine miss or something. But RPM doesn't dip and no sounds. Can't feel any vibrations at high speed (but if I am at lights and take RPM to say 2K and it does "the issue" the RPM needle will dip). Does it in neutral, parked, gear. Sports, C, eco, etc. The car performs well at all other times except idling/startup. It doesn't do it every time I idle at lights (maybe 25-40% at idle), but does it 99% of the time when starting up.

Took the car back to the dealer and after 2 days of diagnosis they said the engine and transmission mounts needed replacing. This was done and I was relieved as that seemed to be the #1 cause from the forums.

Got the car back and all seemed fixed! That lasted about 2 weeks and now the issue is back! The EXACT SAME THING IS HAPPENING.

Have tried different fuel - no difference.

Reading other threads people are suggesting:

• vacuum leak from intake manifold gasket
• engine harness (oil migration)
• defective intake adjuster

Any ideas on where to go from here? Could they have used defective mounts? Some how not installed them correctly? Just so weird how it was seemingly solved after they had it (and did the mounts), and now it's back a few week later!

No codes, no CEL, ever. Oil level is good. 50K miles.

My ML63 vibrated like crazy all the time. No codes, No CEL, and RPM stable. The vibration got worse by time, then I got a CEL and codes. The issue was a defective intake adjuster that would not lock anymore. The adjuster caused the camshaft to go out of timing until it went off enough to throw a CEL. Replacing the intake adjusters on both sides and setting up the timing fixed everything. Now the engine idles smooth as can be.

Good luck.

Thanks! Could the above be the reason that the issue seemed resolved when I first got the car back? I know they had to reset some sort of "timings" when they did the mounts, so maybe they were reset and it was OK, then the faulty adjuster put the timings out of whack again, and so the issue returns?
Cheers

@mdotk It is a possibility.
Two years ago when the vibration started, it would come and go. Sometimes at idle, the next day no vibration. It got worse and consistent with time. I believe as the internal adjuster plate wears down, the internal sprocket does not lock and keeps hitting the outside adjuster sprocket (shell ) back-and-fourth. This caused the cam to go out of timing during a cold start enough to throw a CEL + 8 codes. Even then, the vibration was severe yet the RPMs remained steady, this might be due to the imbalance between the two banks, and the cylinders fighting each other.
Regarding setting the timing, I think in your case they performed "Flywheel adaptation" thru SDS.
This procedure is performed after replacing:
Motor mounts
CPS sensor
After a misfire code
ECU
Since usually replacing the motor mounts does not require setting the engine timing.
If you want to make sure everything is in order, you can perform a test in SDS to check the operating parameters and the camshafts position.