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Another update.
I do think this car is possessed.
After loads of measurements I thought I'd try and get the engine up to temperature - as there seemed there was nothing else to do / measure / kick.
Effing thing started to wildly rev between 500 and 1000 rpm as it got past about 60 degrees C
(So there is an effect from the vacuum switch over valve on the head)
After a few blips from the accelerator and pushing the clutch pedal in the engine seemed to sort itself out again.
It was stable enough to see if I could change the mixture screw setting (which needs to be done after so much cocking about)
Duty cycle was reading a varying amount around 80% - instead of being STUCK on 80% (which in Mercedes speak is 20% == WOT sensor error) it was MOVING - holy crap I thought perhaps I can at least get the mixture adjusted...
...well - turned the screw 1/4 anti-clockwise - Duty cycle stayed the same - still varying though. Turned it another 1/4 turn - same - and another - same...
...What the Fu.....k...
Stopped engine.
Went for the handy Rick's blip tester.
Connect - ignition on - press button - one blip back - no errors! (Damn thing has never ever said there was an error)
Pressed the button to clear all errors - disconnected
Start car measure duty cycle - now stuck on 99.9% (In Mercedes speak that's 0% == ECU not working)
Crap
Stop engine - disconnect negative battery terminal - count to 455 (swear words used instead of "Mississippi")
Connect battery - start car - measure duty cycle - now at 60% ish - varying nicely
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You'll never guess what I managed to adjust the mixture to 50% !!!!!!!
Holy ****.
I'm off for a beer.
(I still don't think the ****ing thing is fixed but at least that bit is about right)
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