BMW I6 engines have long had very low oil pressures at idle. The M54 (according to Bentley) runs around 7 PSI at idle. It's not uncommon to see 5 PSI at idle on BMW I6 engines. This is very low in the great scheme of things. I'm not sure what the threshold for the light is. It wouldn't surprise me if it was around 2 PSI.
Did they give you the pressure readouts? I'm assuming they followed the BMW protocol and put a pressure gauge in place of the pressure sensor on the motor and verified the pressure. What was it at idle and at elevated RPM? Again, 7 PSI is what you're supposed to be seeing at idle. It should be 59 PSI at elevated RPM.
Raising the idle speed is a bandaid if there is a real problem. The light is there for a reason. Putting a bandaid on the issue to make the light go away doesn't solve this. It just creates a false sense of security.
-Verify the correct oil is being used
-Verify the correct filter is being used
-Verify the oil pressure readings they got and how they were obtained
It seems unlikely that you got a bad oil pressure sensor right out of the box. The more likely explanation is that you actually have a pressure issue, and this should not be taken lightly. It can destroy your engine in short order. Causes can range from a bad oil pump, to the oil pump nut being off the shaft, to worn internals, to clogged oil passages.
Get some more info. I wholeheartedly disagree with the suggestions to raise the idle speed to mask this issue. If the pressure is actually low at idle, it will be comparatively low at elevated RPM. If the pressure is out of spec, the reason behind it needs to be diagnosed.
Last edited by fiveightandten; 06-29-2012 at 11:06 PM.