Many thanks for your replies so far.

I have had the following replaced by new Mercedes Benz parts in the past two years:
Both dist caps and rotors, all ignition leads and caps at both ends of all leads, new injectors and their holders and the seals, vacuum hoses across the entire centre of the engine (the ones that sit between each injector), idle control valve, coolant temp sensor, outside coil, new spark plugs (by way of normal MB service), two new fuel pumps and fuel filter, new fuel pressure regulator.

The fuel system was purged by a Bosch technician who also evaluated the KE-Jetronic fuel injection system. The fuel distributor is running good.

The car runs perfectly at idle or during acceleration, outside of the condition I have raised.

Since I wrote the first post, I have to say the issue I have described has become worse in that the symptoms now start in ambient tempratures of around 19C - quite a signifcant and swift detioration in only a few days.

I appreciate what some say about Mercedes attempting to get money out of me, but I have to say I am not convinced in this particular case, as they are going to fit the EZL for a few days to see if it solves the problem. If it doensn't, they will return the part to Mercedes and it won't cost me a penny.

Grateful for further thoughts.
thanks.