[rcflyers]

When I slow down and stop after driving the car I can hear the turbo spool down but at idle you can still hear it slightly.

According to my OBD reader it seems to be providing 2-3 kPa (0.3-0.4 psi) of boost at idle.

Is this normal?

Does anyone else s car do this?

[Asterix]

The turbo spool down is very easy heard on mine as well, has been since I bought it second hand @126000 km, now done 215000 km, no change in sound. I'm not worried....

Don't know about the idle boost.

[Just Rick]

like asterix,one of mine you can well and truly hear the spool down,never really thought about trying to listen for it at idle,but not being a turbo expert I would say that some small amount of boost at idle would be normal,to have no boost you would have to have the turbo not spinning,so I would say it is normal

[Lorian]

I can't hear mine at idle, but then I never really stopped to listen.

What it'll be showing as boost will actually be the difference between the currently (reasonably high) atmospheric air pressure and the default air pressure reading built in, which will be lower. There is no sensor in the car for atmospheric air pressure so it has to use some default value for the calculation.

[rcflyers]

I can't hear mine at idle, but then I never really stopped to listen.

What it'll be showing as boost will actually be the difference between the currently (reasonably high) atmospheric air pressure and the default air pressure reading built in, which will be lower. There is no sensor in the car for atmospheric air pressure so it has to use some default value for the calculation.

When idling it shows 102 - 103  kPa, when I switch the engine off it drops to 100 kPa

[Lorian]

I guess there maybe some residual boost - I'll see what mine does in the morning.

[Phil №❶]

Correct me if I'm wrong, but 101.3kpa IS standard air pressure.

Air pressure sensing does occur as a result of the MAP sensor, I believe. It is used to sense altitude for computer fuel injection calculation.

[Alasama]

I think this is normal, too.

atmosphere = 1atm = 101.325KPa

OBD reader also has its own accuracy tolerance.

The reading difference of 2KPa or 3KPa is very small and within reasonable range, when idling.

[rcflyers]

I think this is normal, too.

atmosphere = 1atm = 101.325KPa

OBD reader also has its own accuracy tolerance.

The reading difference of 2KPa or 3KPa is very small and within reasonable range, when idling.

Correct me if I am wrong, The OBD reader gets it's data from the ECU which uses the values from the sensors to look up the fueling required on it's maps.

I can just about hear the turbo whirring away at idle, whether it's because the exhaust gases are "powering" it, or the induction air is spinning it is unknown!

[Phil №❶]

That is my understanding of what the OBD does.

I would expect that even at idle, the turbo does spin, but does not perform any work. This would be normal and due to the variable vane technology more likely in this type of turbo. This would also share the exhaust gas heat, albeit quite cool at idle with the whole turbo disk, preventing hot spots.

Can't say I've heard the turbo working under any conditions, idle or load, maybe it's seized. 

Just joking, of course.

[rcflyers]

I can hear the turbo spool up much more when the engine is cold, when warm less so.