BMW Repair: 2000 540i idle problem, water pump bearing, vacuum leaks

Question
QUESTION: hello,
Once the car has been running for at least 30 minutes, once you get to a stop sign, the car will idle low (last line on rpm) to the point of stalling. I replaced the air mass meter, the car now doesnt stall but the idle is still low to where it might stall. I brought it to the dealer, they replaced the engine speed sensor, that didnt do anything.  what else can i do, please help :-(
Dante

ANSWER: Dante, clean out throttle body and check for vacuum leaks and intake manifold backing plate (PCV valve). Check all intake and throttle gaskets.
-Evan

---------- FOLLOW-UP ----------

QUESTION: Hello Sir,
the mechanic replaced the purge diaphragm and gasket, is that the same as PCV valve or intake manifold backing plate?

Answer
Dante, the purge valve for the Evaporative emissions system is completely different if that is what he replaced. The PCV valve is in the manifold backing plate. Did he test the intake manifold for leaks or read out faults. Look at the engine computer fuel injection mixture adaptation or multiplicative values? The dealer can increase the idle speed by upto 100RPM but that usually masks the real problem. Look at manifold gaskets especially if higher mileage and replace the backing plate gasket. A worn belt driven accessory on the engine can also drag the engine speed down (i.e. worn water pump bearing, power steering pump).
-Evan