I do not have a260E so my suggestion cannot be too specific but here goes.

It is apparent that your problem is engine temperature related. Your car must have an engine temperature sensor that provides input to your fuel injection computer. On my car (1989 560SL) it is located on top of the engine in the vicinity of the mass air sensor. Replacing that temperature sensor cured very similar symptoms in mine.

There are probably several temperature sensors under your hood, one for your auxiliary fan, one for your temperature gauge and that one. The fuel injection sensor has two wires whereas the others have one and three wires repectively. Remember, we are talking different cars here so you will have to look around or consult whatever maintenance aids you have. I use ALLDATADIY and a maintenance CD.

Good luck Pal and I'm sure we would all be interested in the results of your fix, whatever it is.