Your problem sounds a little similar to something my 190E 2.0 has started doing just recently. Mine's not quite as bad as yours - the problem goes away once the engine is warm, but sometimes when cold it's bad enough that the engine will stall.
As sbourg says, it seems like a lack of enrichment under acceleration (I'm guessing even more enrichment is needed when engine is cold - hence why it's a bigger problem for me when cold?
). I have also noticed some knocking/pinking under load when the engine is hot - also a symptom of lack of enrichment??
The EHA I believe is a little - usually black - device attached to the side of the fuel distributor, if that's what it's called. I'm not good with part names. It should have a 2 pin plug going to it. It's kind of the engine electrical component that's attached furthest to the back driver's side (in the US) corner of the complete engine. If unplugged the car should be crap at starting and die/stumble when you push the accelerator, more so when cold. This is certainly the case with my 16v when I unplugged the EHA.
You can measure current through the EHA to see what it's doing but it gets a bit involved for me at that point!