1998 Oldsmobile Alero codes

Well not to long ag o my car displayed symptoms of a bad maf sensor ad of course the light was on. Then I replaced it and the car rides good. And the light sometimes comes on then goes out intermittenly. I had the code checked and it keeps saying fuel pressure too lean. Then the light goes back out. Then I had mechanic say that my fuel pressure regulator is going bad. And now thats what im going to replace. Please help me through the madness?