My 300E(2.8) developed an ugly surging at idle a couple of days ago, which got progressively worse. Air/fuel mixture is very rich, car is visibly smoking (smoke is black however, sign of overly rich mixture). I have retrieved the fault codes yesterday from the 16-pin connector:
Pin 6-- 3 blinks, followed by 8 blinks and then 9 blinks.
Pin 7-- 1 blink
Pin 8, 10, 14 no response.
Pin 1 is ground, Pin 16 is power.
Erased all the codes, drove the car at least 3 drive cycles and checked the codes again this afternoon after I changed the oil.
This time:
Pin 6-- 1 blink
Pin 7-- 13 blinks
Pin 8, 10, 14 no blinks.
Removed the connector from the coolant temp. sensor checked resistance OK. Removed the connector from the fan switch resistance is OK. Removed and replaced air intake temp. sensor, not sure about checking though.
Drove the car around the block seemed OK. No surging.
Checked the codes again.
Pin 6-- 1 blink
Pin 7-- 1 blink!!
Code on Pin 7 disappeared on its own!
Pin 8, 10, 14 no response.
However after checking Pin 7 the little red led on the air recirculating switch on the dashboard started to blink. What?!
The car does not have factory alarm installed and in any case the ignition was on. And if I start the engine without turning the key to the left first, the heating /air-conditioning does not work. After restarting the car it works again. Strange.
Now the surging is back, the air/fuel mixture is very rich, car is running very poorly. During code checking on grounding Pin 10 an audible click can be heard from around the throttle control area.
I am not sure what it is.
This is where I am standing right now. Any help or idea would be appreciated. The car just went through a major tune-up; every maintenance item was changed.
Sorry for the winded post, tried to be as clear as possible.
Thanks for your help,

Alex