If it is only on acceleration then it could very well be that it is getting too much fuel (max fuel delivery too rich). This was the case on my 240D such that when you pushed the throttle down to accelerate it opened the IP all the way and it was dumping too much fuel so that it couldn't burn it all.

I admit I know nothing about your motor or car though so this is just a thought... good luck.

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique