Hi everyone
Am a first time Benz owner, bought 2015 ML 350 4matic at 115k miles.
Noticed the engine has this rough idling (also vibrates) during cold start. But after it warms up and switched off for about 20-30 minutes, the rough idling/engine vibration clears when you start the engine again.
I earlier suspected a faulty ignition coil, so we changed for bank 1 & bank 6, but the situation still persists.
I will appreciate some advice from your collective wealth of experience.

How old are the spark plugs since replaced?

"bank 6" is Bank 2 cyl. 6, right?

Can you use a scanner to scan ECU... & clear faults?
This will get it to relearn mixtures

Many Thanks Bro, for your assistance

How old are the spark plugs since replaced?
- cant say, only got the vehicle for about 1 month.
- We actually suspected a faulty ignition coil which was replaced but the issue persisted

"bank 6" is Bank 2 cyl. 6, right?
- yes bank 1 and bank 6

Can you use a scanner to scan ECU... & clear faults?
- Ok, i own a Bluedriver scanner, the last scan i did pointed to the injector but a quick check on google suggested poor quality fuel.
- Will re-scan and clear faults then observe behaviour

This will get it to relearn mixtures

Thank you so much, appreciate your support

This is the cylinder arrangement. If you are able to scan your engine control I think you will find misfires on one or more cylinders. Most likely they will not occur above a warmer ambient temperature like 50F

the misfires are caused by lean mixtures from poor combustions: the ECU takes away fuel.
Result in detuned engine power.

Part of that is carboned-up Lambda sensors from engine burning thin oil meaning don't just replace sensors, upgrade oiling as well.

Bro
Thank you so much
Am gathering good experience already.

Appreciate

Thank you for this schematic

Lots of experience here, to use

Just to share feedback
The issue was partly pinned to faulty ignition coil on bank 6.
After replacement of faulty ignition coil on bank 6, i took the vehicle out for a long drive, with several shift down hard driving, the injector issue eventually cleared.
Guess it was some debris clogging the injector, being forced out under pressure during the long drive
I immensely appreciate everyone's contribution on this.