E70 Hi RPM Engine Idle with A/C & BMWWHAT APP Code

[PhastPhil]

Originally Posted by ChuckG

Most if not all cars increase the idle RPM when you turn on the A/C to keep the engine from stalling with the extra load from the A/C compressor.
Chuck

Hi Chuck,
Ever since fuel injection and ECU's, idle speed has been governed by a computer, therefore when an idle speed is set, say 650rpm, adding load: i.e.: drive or A/C, the ECU compensates and keeps the idle at the SET RPM - I'm all for that and it works very well. However, in the E70, when the A/C is on the idle is increased to 900+RPM from the 'normal' 650rpm.

My previous X5, E53, did not exhibit this issue OR our other BMW an E93 328I-C. With or without A/C the idle is steady at 650rpm. And as I noted there is a setting in the BMWAPP coding to reduce the idle speed with A/C on, to normal (650rpm).

When I refer to the low speed dynamics, I feel i'm 'fighting' the car as I slow down, like for a red traffic light or stop sign. The high idle wants the car to move faster than it feels when the A/C is off and the idle is 650rpm. I can modulate the brakes more effectively at the slower idle.

Soooo, the question was: Why did engineering at BMW increase the idle in the E70 to over 900rpm when other similar 6cyl BMW models with same engine, just use the normal idle of 650rpm with or without A/C engaged? My thought was either A/C efficiency or some emission issue.

And as a final note: thinking I was a bit too technical and critical, at a recent visit to the dealer on another issue, another E70 owner was complaining to my service writer about the same issue. It validated my concern.