1991 Chevy Blazer Engine OEM cpu

I took my truck to a shop for them to analyze it becuase it has a sputer when in drive and idealing. I chanked the plugs and wires but still doing it. But he hooked up the cpu to the analyzer and it basically can not cummunicate with the analyzer. Tried it a couple times again after that but still no luck. So the gentlemen says that more than likely means that the cpu is bad or it is going out and he also says that this could possibly mean that this could be the reason for the original problem. Do you agree with what he says could be true? Also with the original problem the voltage jumps up and down while it sputters and the lights dim when it jumps up and down.