thanks for the clarification.

I think I may have figured out the problem, and boy do I feel like a tool. It made sense to me that once changing the glow plugs after 130k miles, that it started worse and rougher because they are pulling more power from the battery. I tested the voltage at each one during the glow plug burn cycle and noticed the it started at 12.5 volts then quickly fell to 9 volts over the course of 5-6 seconds.

this morning I got up with the engine cold and hooked my jeep battery up to the Mercedes battery and "jumped" it.

almost no missing or rough idling.

I think I just need a new battery. the one on it is one that was on the car when I bought it and the guy said he put a new battery in it recently 'just to get by'. he said he couldn't find one that was listed for the car. it only has 615 cca.

what should I be looking for in a replacement battery?

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'92 300D 2.5
'99 E300TD