Thanks to this site I was able to fix my hesitation problem.
I have a 92 400E (M119) 165K Mi. The car would be fine when cold but when it warmes up it would miss at idle specially with A/C on. It would also miss or hesitate when starting to move from stoped position or if tried to accelerate quickely. I changed the distributor caps, rotors, Spark plugs, spark plug wires, checked for vacuum leaks, they made no difference. I did all that repairs over a period of ~ 10K miles. I finally took out the fuel injectores and washed them in the ultrasonic bath with gasoline and isopropanol and after I put the injectors back and started the car it was smooth as it ever been. Before I took out the injectors I used injector cleaner in the tank but that did not do anything.