I have a 1997 Expedition, the check engine light is on and it is idling low. I took it to autozone and they checked it on their machine said thay it is running too lean, it could be MAS or O2 sensors going bad? I had someone else tell me it could be fuel filter, and someone say it could be dirty injectors. Any ideas? It is running rough and shakey at stops. Has not died, but quivers like it is going to. I don't want to get taken to the cleaners so any help anyone could give would be great!