My somewhat recently bought CLK 320CDI had an "allergy attack" the other day and another one a day after. I do realize it's the season for that but...

On a bit more serious note here's what happened:

• Start the engine (in both instances the engine was lukewarm, neither cold start, nor started after a brief stop)
• The revs start jumping up and down between 300-800 rpm viciously, blueish smoke spewing out from tailpipe heavily, car is noticeably shaking (coughing)
• Any throttle input does absolutely nothing, maybe adding more exhaust smoke (but can't confirm), shifting between park/drive/neutral has no effect.
• Turn off ignition, restart the engine straight after - runs completely fine in both instances.
• Recently I've changed engine oil and air filters; oil level is just a hair width above the max on the dipstick (doubt that could be significant enough for the engine to start picking up excess oil), coolant level looks unchanged, checked air flow sensors - replaced correctly, filter casings sealed tight.

Looks a bit like fuel deprivation to the engine, but that does seem odd that upon restarting it runs fine, also flooring down the throttle makes no effect and additionally when running normally and flooring the throttle it launches as I'd expect.

Any ideas? Anyone encountered this issue before and like to share their experiences?

Blue smoke would generally indicate burning oil. I;d check fuel pressure - maybe a bad pump.