Engine not revving properly - Mass Air FLow issue?

[sunny5280]

Originally Posted by treeman

X5 running sweet - I forgot how nice it runs when everything as it should be.

Indy changed the middle pump and all is ok.

I have been told before by my BMW dealer mechanic that my age X5 (2003) can throw misleading error codes (i.e. Air pressure code displayed when it was the fuel pump failing). He explained that in 2003 they where only just starting to use computerized error coding and although sometimes helpful he said they where often misleading. This was when one of my injectors failed but the error codes thrown up then said nothing relating to injectors being at fault.

Anyway thanks for all the help. especially to the two of you who did mention Fuel Pump as a possible cause - It does show though how misleading the error codes can be as having mentioned the Air Pressure error code and the first 3 mechanics diagnosis that it must be Air pressure related I pretty much forgot to pursue the Fuel Pump possibility.

Diagnostic codes are meant to assist in locating a problem. They are set when a sensor detects an out of specification condition.

Without knowing the specific codes you had I can speculate a low pressure fuel condition could cause an air monitoring circuit to read an out of specification condition. As fuel pressure decreases the amount of air in the air / fuel mixture could increase outside of acceptable parameters. Often times this results from an air leak and thus a misdiagnosis occurs because the mechanic is investigating only one of the causes.