Pontiac Repair: One Cylinder Not Firing, pontiac sunfire, piston rings

Question
I have a 1995 Pontiac Sunfire (auto.) that started fine the first time started on Sunday AM.  Next time when started it began to idle rough and sputter, especially more so when A/C was on.  In the shop currently, where they tell me one cylinder is not firing, but they do not know why.  They changed coils, plugs and the fuel filter is fine.  Can you offer any suggestions?  Car has over 180,000km on it.

Answer
Hi Shelley:

well in order for an engine to run correctly it needs 3 things. spark,fuel and compression. the spark could be a plug,wire,coil or module. The fuel could be fule pressure bad sensor or bad fuel injector. The compression is an engine mechanical issue it could have a bad valve,or piston rings. Without seeing this or knowing what codes if any are in the computer system it's really hard to tell you exactly what the cause could be. One think I can tell you if this car has that many miles on it I'd think long and hard before I sink any large amounts of $$ into a repair.