Hello there, my 2009 XC90 with B6324S gas engine 3.2.started whistling between 800 and 2500 RPM. Sounds like a turbine, which I do not possess
O2 sensors report lean mixture error codes. Long term fuel trim is close to 30% while short term trim is very low. Hence the check engine. Starts well when cold, on warm will crank forever, might not start. Fuel pressure sensor reads around 50 bar, so we are good there. At idle, when removing the oil filling cap there is barely any suction.
Blew propane around the engine and manifold, no impact on RPM.
Blew some smoke into the air intake tube after the airflow sensor - no smoke comes out, which leads me to suspect that the vacuum leak is somewhere behind a membrane or a solenoid.
Replaced mass airflow sensor, replaced PCV cover with membrane without any impact.
Now I am suspecting the evap system leak, but not sure where those hoses are on the 3.2. and the location of the whistling sound throws me off as in driver's seat the whistle locates somewhere right at the engine, not behind me or under.
Any suggestions from past experiences with this engine?

 

what happens if you pull the dipstick out - does the whistle stop? you can try listening with a hose (poor man's stethoscope) to see if you can pin-point the location.

 

No change. Dipstick out or hole plugged, still light whistle.

 

Can this be whistling throttle body?