On my 2003 4 cylinder optima, it wouldn't start. Would crank but not turn over. One month before, the same thing happened so my mechanic replaced the fuel pump and strainer, cleaned my tank and all was good except for hesitating and rough Idling. Replaced the coils and injectors and was all good. This time we replaced the entire fuel pump assembly because some of the clips and wires were close to breaking. No start at all. Will start with starter fluid and then stall . Code showed low volume mass air flow sensor. Replaced maf. No difference. Any ideas? My mechanic is pulling his hair out. Thought there was a 2nd fuel filter, but after following the lines from the pump to the firewall, found nothing. Help!