80 series Flat Spot

I have a 94 model 80 series petrol Cruiser, the engine has a flat when I lightly accelerate after
backing off and removing my foot from the accelerator. I have had the vehicle to Toyota who
plug it into their computer and tell me everything is normal - this is not so.

I had Toyota do a hot flush on the fuel system which seemed to solve the problem but this only
lasted about three weeks before the problem was back.

Has anyone experienced this problem or more importantly know what the solution is