Just to throw another possibility out there: My '88 260 would hesitate badly in cold weather. Start up was fine, but as the coolant temp went up and the engine controls went to closed loop, hesitation would set in.

I checked just about everthing before finding that the EHC was the culprit. The clue was a slight gas smell under the hood after driving caused by a crack in the EHC. The leak was not big enough to see any fuel, but you could smell it. I would definitely suspect the EHC if you have a fuel smell around the EHC.

Bad news is that the part is expensive. I found a new Bosch one on EBAY that was just fine and not too pricey.