Rough warmup during cold engine - 190E 2.3

my car (Mercedes 1985 190E 2.3 with 109K miles) gives me a very rough time on a cold engine - it misfires, sputters, kind of coughs all the time - no pickup, almost stalls. The moment the engine is warm (80
degrees C on the radiator temperature), it runs smooth as butter. Problem started 3 weeks ago, and is very consistent. What are the possibilities - what should I do - will it ruin my engine if I continue driving like
this (as long as I warm up the car everytime)? Or is it just old age problems with a 15 year old car and I should ignore it?

I would really really appreciate your response. My casual conversation with many people reveals that this is a very common problem, so many readers would benefit
by your answer.

thanks a lot.

A. Gupta