The car is now fixed.
I purchased a fuel pressure gauge and discovered that the control pressure was very low. The misfiring was resolved by adjusting the warm up regulator to the required pressure.
Take aways:
1. A bad misfire isn't necessarily an ignition problem.
2. Not all Mercedes specialists are really 'specialists'.
3. If you pay a mechanic to check something and they say it's ok, they might be lying.
I purchased a fuel pressure gauge and discovered that the control pressure was very low. The misfiring was resolved by adjusting the warm up regulator to the required pressure.
Take aways:
1. A bad misfire isn't necessarily an ignition problem.
2. Not all Mercedes specialists are really 'specialists'.
3. If you pay a mechanic to check something and they say it's ok, they might be lying.