engine idle

[stu412t]

hi i have a 1991 520i when i remove the oil filler cap with the engine running the revs drop is this normal????
stuart

[DaveVoorhis]

It's normal.

[632 Regal]

perfectly normal and showing you that there arent any major gasket leaks.

[Barney Paull-Edwards]

Correct, but I assume you did it" because it was there"! Emission control gear causes that,ties up with another thread about cleaning emission parts.Do not take off brake to servo pipe as it will cause engine to run very lean,If you have old-fashioned stuff called REDEX (ask your father) then simply pour it into the intake,pause , and rev the nuts off the engine, all the crap on your valves and intake butterfly will go through the engine thoughly pissing off the neighbours but cleaning out the engine.

[baksa]

hi i have a 1991 520i when i remove the oil filler cap with the engine running the revs drop is this normal????
stuart

And what if revs do not drop and engine works the same with or without filler cap?

[DaveVoorhis]

And what if revs do not drop and engine works the same with or without filler cap?

Put your hand over the filler hole. Does the engine try to suck it in? If not, you could have a vacuum leak in the intake.

[baksa]

Put your hand over the filler hole. Does the engine try to suck it in? If not, you could have a vacuum leak in the intake.

OK, I'll try that, because my M50 engine sounds and revs the same with and without cap.

[Barney Paull-Edwards]

Dead right,if revs do not alter you have probably got a blocked pipe or manifold leak,is mpg ok? Not sure about your rules reference Emissions but you will not pass a roadside check like that,for manifold leak, do the "easy staRT" spray trick,if revs go up theres your problem if not its the pipework.