[buzzinhalfdozen]

Randy, yes get out your tester, lets look at the easiest stuff first. Though there is an almost unlimited list of things that could be causing your issue I like to start with the simplest things first. The tach and datalogger both showing eratic engine RPM in my mind indicates an ignition issue. Posts indicating interference are of interest, any signal getting into the box can cause problems. Have you changed the routing of any wires on this car? Alts. fans,coils ect. too close to the trigger wire can "leak" into the wires. Twisting the wires is a good idea though most are already twisted. Joe