My car starting running rough and and had very little power after I started it and turned a corner. the check engine light came on and it said drive slowly to a stop.. I pulled into a shop that scanned it and they said it showed misfire code #3 cylinder not firing properly and catalytic converter code. We replaced the spark plugs and boots with volvo recommended parts and it still runs rough. There is no smell from the catalytic converter. I replaced the fuel filter several years ago. I replaced the thermostat recently also. What else could be causing the car to run rough. The shop said the catalytic converter code could have been caused from the thermostat going bad or the spark plugs. One owner car I have had no problems with until now. Thanks for your help Tina