I didnt say to just replace your factory tach with an aftermarket one, just said that in hopes that'd youd use that to help you narrow your search a bit. My factory tach does the same thing, and its either a short somewhere between the firewall/connector or the cluster is going bad (which I could believe.... dash lights keep going out and upon fist-impact they turn back on)
cps- camshaft position sensor? Or Crankshaft Position Sensor? Being a '92 s'ploder... itd have the Crank sensor. You'd think if the crankshaft sensor was going bad, youd have a CEL on, and possible no-start/rough running situation. As the crankshaft sensor tells the PCM where the rotating assembly is in its rotation in relation to ignition timing. Or something like that.