Mercedes R Klasse Cold Start Problem

Hard starting and a rough idle on cold starts definitely points to fuel delivery issues. A faulty injector makes sense. I would suggest running an injector test to confirm your suspicions. It could also potentially point to other issues, hopefully its something minor!

Could you elaborate on how to perform this injector test and what I should be looking for as an indicator of a defective injector? I'm trying to avoid unnecessary trips to the mechanic.

While there are DIY injector tests, accurately diagnosing individual injector performance often needs specialized equipment. Given your symptoms and mileage, a professional diagnosis is advisable. They can accurately assess fuel delivery and confirm if the injector is indeed the culprit. A workshop will also be able to test fuel pressure and flow.

I took the vehicle to a workshop, and as suspected, the injector was indeed defective. The eventual repair cost was 515€. The hard starting issue is now resolved.