How long since a tune-up? Use a gage and check fuel pressure. Any applicable trouble codes? An intermittent rpm signal can drive you crazy. That signal comes from crank sensor. I can't be positive that is the problem?

To check codes, you can use jumper wire between A & B terminals at the datalink connector. Turn key just till dash lites come on, no further, no crank. The mil starts flashing, you count the flashes to get the codes. Your looking for two digit codes. There may be more than one code, so you have to watch.