ok, the car is a 190e-1,8 litre-uk spec-112,000 miles on the clock

how often does one replace the distributor cap/rotor?-i think the previous owner changed these items at the 80k mark.

the only problem i have is an uneven idle for 2 seconds or so on cold start-up

If it smoothen out after that and engine keeps a steady idle rpm I wouldn't consider this a problem.

Or has it started doing that recently?

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'87 MBenz 190E 2,3 8vlv

yes,it smooths out after the initial 2 seconds or so of rough idle after a cold startup.