Have a helper crank it, while you visually check for spark at the plugs. If you have spark everywhere, use a gage and check fuel pressure. Some of the national brand autostores used to loan out a fuel pressure gage, if you don't have one. To check for spark, you might disable the fuel system. If there are plug wires, you can take a plug wire loose from the plug, use known good plug or spark tester in the boot, ground metal part of plug/tester to metal part of engine, engine cranking, watch for spark. If the ignition module assembly sits right on top of plugs, there are no plug wires. You can turn the assembly, up-side-down. Use a spark tester in each boot, use wire to ground metal part of tester to engine block.
My first thought was an intermittent rpm signal, can't be sure?