325 runs rough when she gets hot

[fun4eva]

Hello everybody !

I have got a 1992 325 with the m50 engine. She runs OK until the temperature gauge gets to the middle,then she runs rough, engine shakes etc.... won't stall though , it idles good.Could it be coolant problem? I had problems with heating this winter since the engine temperature never went above the blue section, only when I wasn't moving for a while ( that time I had heat).I think thats probably a thermostat issue.I flushed the system, there was a lot of dirt in it but no improvement.I also thinking maybe a spark plug / coil problem or catalityc converter? What else it could be?
Any help or idea will be greatly appriciated.
Thanks,