E220 cdi - Engine speed at idle

[grufflybear]

Hello... just wanted to compare notes with other E220 drivers - mine is 2007 220cdi auto -25,000 miles and running silky smooth but I am curious about the idle speed... sometimes it seems to be just over 800 and sometimes just below - next service is not due for ages yet and maybe I haven't really noticed before - If it is idling at just under the 800 and you switch on air-con it increases to just over 800 which I would expect but after a while it drop back - it is smooth at idle and only really notice in stop start traffic - Perhaps warmer weather means car is adjusting slighlty lower with warmer inlet air or something ???? I am almost sure that aftyer it was last serviced the idle speed was around 825 when the engine was warm regardless of air-con etc Anyway I like to understand things so just a casual thought for a Sunday morning

 

[corned]

The compressor doesn't run all the time under load necessarily. It is governed by a thermostat somewhere. Are you sure this isn't simply due to the compressor kicking in and out occasionally in normal operation.

If you switch the aircon (or the whole Thermatic/Thermatronic system) off, what then?

 

[pkp]

How does one find out if the idling of the engine is correct? I had requested a check of my engine settings as when I accelerated, the needle went vertical up, without the speed increasing significantly. The MB service, I reckon increased the idling as I could hear more idling noise, and now I fear my MPG has gone down without any noticeable change in acceleration.

 

[Joesoap17]

pretty sure idle speed is 825 and may increase under load i.e. aircon kicking in. The idle speed is set by the ecu and depends on a range on sensor info.
As regards your increased revs with slow road speed response I would get the auto box ATF flushed and filter changed. go to a gearbox specialist or an Indie price should be around £250