Stalling

I have a 1984 380SL with 75,000 miles on it. I have not had any problems with the car since I bought it two years ago. Last week it started stalling right after you start it and put it in gear. Sometimes it starts right up and other times it is very hard to start. I replaced the fuel pump relay but it made no difference. It does not make any difference it the car if hot or cold. I am planning to replace the fuel filter as my next step. I would appreciate any help I could get to return this car back to a reliable weekend fun car.

Thanks, Tom

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