Got a problem with my 91 420SEL (85K) miles. When it is dead cold it starts and runs fine but in the warm up process at approx. 70 degree C, it hesitates and does not want to take the gas. Once the temperature goes up a few degrees the problem ceases. It does not reoccur for the rest of the day. It has to sit over night before this condition can be duplicated. Have checked all thermo-valves related to the problem or not and vacuum circuits. It was time to replace the distributor cap, rotor and plugs anyway but this made no difference. Have read on line about others having this condition but never found a remedy. Contributors to lists have said that the CIS-E goes into closed loop at 70 degrees C and it may not be a smooth transition. Seems with my car that it is getting a signal that it has warmed up a little too soon and the engine does not like the fuel mixture. Rather than test the temperature sensor reporting to the CIS-E, I just replaced it. No difference. Does anyone out there have experience with this problem?
Thanks for any help.

Bob /San Carlos, Ca.
78 280CE
91 420SEL