I replaced the alternator. Changed the O2 sensor. Sometimes it seems to run fine then it runs bad. It ran fine when I took it to my mechanics shop for a tec 2 scan, then ran crappy all the way home. My wife says it is now stalling in traffic. Happened today while she was turning. Lost power steering and almost went into the ditch. I have read so much all over the web that I do not know what to do. Only code is P0300. Help.