Climate control increasing idle

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hiya
i have a w211 220 cdi with same problem,i wonder what happen with yours
 
in another forum someone said it could be faulty ac unit sending signal to ecu while ac is not on and that would be the reason,thats why i wanted to find out because there is a leaking with my unit and maybe its a pressure relating problem
 
If your A/C is leaking. It will soon stop working. As stated several times this is normal behaviour. The ECU will try and either heat or cool the car to the selected temp. It will also do this dependent on other factors.

Do you have UV Protected windscreen?
Have you got tinted windows?
Is the A/C set to auto or manual?
Have you got a window or door open?
Any leaking door/window seals?

As soon as the car detects load it will increase and decrease revs accordingly. I have three Mercs and all do the same. Just to check so does my Japanese Pajero.
 
My W211 is exactly the same and it means that when you are stationary, the car is pulling forward more than it should. I had mine checked on a STAR, a faulty fuel heat sensor was found and replaced, but it made no difference.

In winter it is constantly @ 850 rpm if the heater fan is on its lowest setting without aircon. I can turn on both front seat heaters and heated rear window without an increase in idling speed, but as soon as I turn the fan on even to its lowest one-bar-setting, the idling speed increases.

At this time of the year, once the engine is warmed up to around 80°, the idling speed will drop to 750 rpm even with the fan on.

I had this advice from an expert:

The idle speed control on the 646.821 keeps the idle speed CONSTANT even under load requests such as AC or drive position!!

The ECU controls the Idle speed by receiving sensor data from---engine speed(CPS), coolant temp(CTS),accelerator pedal position(APS), and fuel rail pressure(RPS)-------therefore either the ECU or relevant sensors should be diagnosed to determine why the drastic change in idle speed!!-----either live with it or make the investigation a weekend project for the grand kids---they love electronics and can sort out anything!!

This is not a DIY unless you have a copy of DAS Xentry!!

I too would be grateful for a solution; it IS a problem and NOT normal.
 
So it happens on every car. you've been assured it's normal, but you managed to find an 'expert' to tell you it's a problem, hence you worry about it.

Wow, I wish I needed problems this badly!
 
bozmandb9 - I don't understand why you have written this:

So it happens on every car. you've been assured it's normal

Who says it happens on every car and is quite normal?

I just wonder if you have a bridge to look after and you try to deter billy goats from crossing it.
 
On the w211 the humidiTy sensor makes the ac compressor kick in even if ac is off. That explains inclination etc. the sensor is in the evaporator. It can be disabled via star but you need to know how ... It has to be set to absolute rather than relevant. I dont. Lol. Depending on settings when the compressor engages rpm may rise. Hahahaha. Oops sorry.
 
And of course rpm rising due to compressor engagement due to humidity, is a different matter from rpm rising due to low ambient temp vs hvac settings!
 
Hi all. I know it's been a long time since the last response to this thread, but now is happening exactly the same to my car (W164 ML280CDI)

Does anyone found a solution for this issue ?

Thanks,
Antonio
 

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