I replaced my O2 sensor in hopes it would fix my little problem of miss firing. It didn't, but when I started my car I let it idle and usually if I haven't driven it and I let it idle it stalls out. It stalled out, then I checked to see if it was throwing any codes and it wasn't. Is that usual? Or is there something wrong with the ECM?

 

Sometimes the Idle Air Control gets fouled out. I would take off the Throttle body and remove the IAC below and clean it out. Get a new gasket while you are at it.