First my car started out with a contineous memory code of 172. I tested everything it could be but everything checked out. So I figured it to be the o2 sensors which checked out fine. I swapped them to different sides then got a code of 543. Now I know this code deals with the fuel pump/pcm, though it can be from a bad o2 sensor also. So I replaced the o2 sensor and it ran better. Now every once in a while if feels like the fuel system is shutting off for a split second. Though now codes are found. I replaced the fuel pump relay but still the same problem. It feels like a misfire but happens so rarely its hard to pinpoint. Yes it could be the fuel pump but that tests out fine also. Maybe its the PCM?? Also when I start the car when it is cold it misses at idle. Then once it warms up a little its ok. I have checked out every possible scenerio on both these issues. If anyone has some ideas that I may have missed please let me know. Thanks much!!