Just lately after the car has been running for 30 minutes or so it stumbles a little starting from a red light. I'm assuming its an ignition problem, and not mounted on the engine since it takes longer for the engine to warm up before it stumbles. It's a 1991 190E with a 2.6 liter M103 with a 5 speed standard transmission, and has a newer (since December) distributor cap.

what could I check and what could it be?

Thanks

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5 speed '91 190E 2.6 320,000 mi. (new car, fast, smooth as silk six, couldn't find any more Peugeots)
5 speed '85 Peugeot 505 2.5l Turbo Diesel 266,000 mi. (old car, fast for a diesel, had 2 others)
5 speed '01 Jetta V6 (new wifes car, pretty quick)
5 speed '85 Peugeot 505 2.2l Turbo Gas 197,000 mi. (wifes car, faster, sadly gone just short of 200k )
5 speed '83 Yamaha 750 Maxim 14,000 mi. (fastest)
0 speed 4' x 8' 1800 lb Harbor Freight utility trailer (only as fast as what's pulling it)