It is possible that after the previous problem the fuel mixture adaptations were not reset. Logically a car with a bad fuel pressure reg was being adapted leaner (normal problem is a leak which makes it too rich). If the problem is corrected without changing the adaptation the car will continue to subtract fuel until readapted. On your car that can take weeks. It should happen eventually even without help, although it is real easy to set other "Check Engine" problems in the mean time.

I would ask the dealer, although the service writer probably won't like it with you knowing more about it than he, so go gentle with him.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician