Ok, this has been going on for quite a while and its getting a bit annoying...I will be driving down the road or sitting at a light and my car will just quit randomly...even on the highway at times or going up hills... Takes it a few minutes but then it will usually start back up. (although a couple times it wouldn't start and we noticed that we had loss of power inside the car, like door locks, windows, and no dash lights). Has been doing this for the past 6 months but lately it seems to be doing it a lot more often. Throughout this time, my check engine light has never came on. We did the key trick and got a code 12 21 21 55, was going to go get an O2 sensor but my step dad advised me not to saying that it wouldn't solve my problem so we didn't. The next time it died, we checked the codes again and now the codes are only 12 55. A couple weeks have went by and that is still the only codes we are getting. My boyfriend is not a mechanic but he tries hard to fix things. So far hes replaced the ignition switch, crank shaft sensor, and the AIC module, cleaned the MAP sensor, tested the cam shaft sensor, the MAP sensor, and checked for loose wiring and looked for vacuum leaks. All the tests were good showing the right voltage like the book told us plus we have researched some stuff online. We also went to a mechanic shop and had him hook my car up to a computer and to test our fuel.....hooking it up to the computer showed nothing wrong and he said that everything was good with our fuel..... My car hasn't failed to start yet since we replaced the ignition switch and plus we haven't been having power issues any more but it still stalls on us.....its weird, like if we just let it idle for awhile then all of a sudden it will idle too low and die. We have talked to a few friends that work on cars and they said its sounding like its the module which is actually located in the PCM on my car.... I don't have the money to just go throw it around on all these different parts so I just wanted to see what your guys' input was on that...I'm a poor folk so if that is the problem, I guess I will be saving up some money to replace it. I am just exhausted stressing about this car all the time...I'm a full time student, work, plus a mother of 3 children so I really need my car fixed. All input is greatly appreciated! Sorry for the length, just wanted to make sure I include everything that we've done or noticed.