[MR2] Then, too I am forgeting firing order

[William Brandt]

so 2 pistons can't be having a power stroke at one time. But almost every design I have seen shows to pistons moving in tandem for balance. '

In inherently rough engines they will use a balance shaft acting as a counterweight to the crankshaft - Porsche in their 944 and Mitsu have used balance shafts. 

To my knowledge Toyota has never used one. (which is a good thing!) 

Bill