C4 INTERMITTENT DROPPING OF CYLINDER

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I have a 1988 C4 with 30K original miles on it. History is the car sat for many years in a climate control garage and never moved. Since then I have literally replaced everything from the headlight motors, to the master brake cylinder...Although it most of the time runs like it is new, I have been having an intermittent dropping of a cylinder for over eight months now, in which the car, always after being driven, turned off, parked for an hour or less and then started will start dropping a cylinder. The problem now lasts about five minutes or so, and then suddenly disappears. It does not seem to be a daily problem, but is a weekly occurence. In order to try and resolve the problem, which was much worse (dropping of cylinder used to last almost an hour and happened daily) I replaced the ECM which greatly reduced the problem but did not solve it. I have done the following to the car so far: replaced all plugs, wires, distributor, gas filter, had injectors cleaned and serviced, fuel injectors all replaced, one of them had to be replaced twice because it failed and is now the only NON ac delco injector, replaced all the fuel rails, placed bg gas additive to attempt to further clean the fuel system. The car is throwing NO codes, and was not throwing any before I replaced the ECM. The one non-ac delco injector was just checked again friday and it is pulsing properly and shows no signs of malfunction, along with the other injectors.

Does anyone have an suggestions.......to permanently cure this annoying problem?.....I would appreciate any feedback...thanks fred.