Other possibility (although less likely since I only know of it happening on a couple of SLC 43s in the US) is a software problem that requires reprogramming to prevent misfires. My 43 had it and it was diagnosed by moving the spark plugs that had the misfire codes to different positions. Misfires happened again so they knew it wasnt the spark plugs but rather a software problem. I THINK it was specific to the transmission, though, so theoretically a 300 could have it with the 9g tranny. For me it always happened on hard acceleration (pedal planted) and moreso going uphill and hard accelerating at the same time.
Interesting re-reading this post:
While away last month on our group Euro Road Trip down in the Alps, I got the Engine Management light come up and also the engine felt lumpy as though it wasn't running on all cylinders....
> It happened after applying power after a section of down hill Engine breaking..
> Was un-likely to be fuel quality related, as had ~25% plus fuel load & had filled it full with 98 octane fuel at the last fill a few days before.
(So could have been fuel starvation? as happened after a long sweeping 520' corner that spiralled under it's self through a tunnel - See map below..!!)
> Engine + Oil temp was normal & only ~23'c out side temperature.
> Pulled over straight away, took the key out and started again fine & haven't see the problem again..
> Luckily @Col
was able to plug in His code reader in the next day & pulled the following codes - Google'd them but not able to say exactly what they are for My R172, which is newer that the SW on Col's code reader:
* P030022 - Possible coil pack..?
* P030200 + P030300 - Possible cylinder misfire codes..?
Will get MB to look at these at some point, as the car is still under warranty, but thought I'd document it here just in case other owners have or have had the same problem:
Map of the bit of road I was driving at the time the EML came up: