[BlueTangClan]

When my AC is on and I release my brake from idle, the car jerks forward a little bit even if I try my best to release the brake as slow as possible. Is this something that can be fixed?

[HighlandPete]

Originally Posted by BlueTangClan

When my AC is on and I release my brake from idle, the car jerks forward a little bit even if I try my best to release the brake as slow as possible. Is this something that can be fixed?

Are the idle revs increasing (200rpm) when A/C is switched on? If so, possibly causing the issue with the jerky move off. Energy management could be involved.

If the above fits, may be worth switching off other energy consumers to see if the revs stay at the normal idle with A/C switched on. If back to normal, could be battery condition, or simply battery draw and the alternator load requiring extra revs.

[BlueTangClan]

Yes the rev increase a little bit when the AC is switched on, but I thought that's normal. I've attached 2 pics. The left is AC off, the right is AC on.

What do you mean by "switching off energy consumers"?

[HighlandPete]

Originally Posted by BlueTangClan

Yes the rev increase a little bit when the AC is switched on, but I thought that's normal. I've attached 2 pics. The left is AC off, the right is AC on.

What do you mean by "switching off energy consumers"?

The higher revs explain the gearbox behaviour.

Are you running high electrical loads? Lights, high A/C fan speeds, etc. If you can switch anything off, to reduce the electrical load, see if the revs will drop back. Nothing lost trying.

If no change, it may simply be the A/C load causing the need for rise in revs.

[BlueTangClan]

The fan speed is at the lowest setting. There are no lights on. The only thing on is the auto headlights. When I switch that to off, the rpm doesn't go down.

[HighlandPete]

Originally Posted by BlueTangClan

The fan speed is at the lowest setting. There are no lights on. The only thing on is the auto headlights. When I switch that to off, the rpm doesn't go down.

Another factor I never mentioned, is the load on the A/C and cooling fans due to ambient temperature. If you have a high demand on the A/C, then you will likely have the increased rpm.

Back to the transmission, it will be those extra revs which are starting to engage the torque converter, causing a bit of a jolt.

[BlueTangClan]

So is this normal, or something that can be fixed?

[HighlandPete]

Originally Posted by BlueTangClan

So is this normal, or something that can be fixed?

Increase in revs, Idle Speed Boost (up to 200 rpm increase) is part of the energy management.

Out of interest I tried my 535i this morning. No change in engine rpm, switching A/C on or off. The demand on my A/C was minimal, ambient temperature was 9C, no requirement for the engine cooling or A/C fan speeds to pick up.

[The_Transporter]

Tried this on my 2012 550 today. I tried multiple things such as ac, lights and radio all off and then all on with ac at full cold and then full heat. All with zero change in rpm. That said I guess under other circumstances I could maybe see a slight increase due to power consumption but 200rpm seems very excessive and not normal at all. I have had cars in the past that when I put a taxing power load on it the rpm would increase by maybe 25-50 but never anymore. I would get that looked at.