Well 250,000 miles and still going. It has started acting up once warmed up. It will jump to 1500 RPM’s then drop to about 900 then back to 1500. up and down up anddown constantly. It does run smooth down the highway and still gets about 30MPG. Has new plugs, pcv valve an air filter. Vacume seems to hold as I can set cruise and it holds. I hope you have some ideas(Helpful ones) Thanks Jim
You MAY have a faulty TPS (Throttle Position Sensor).
A broken or loose TPS can cause intermittent bursts of fuel from the injectors and an unstable idle because the PCM thinks the throttle is moving.
When’s the last time you replaced the thermostat? I had an '85 SEi Accord with bouncing idle and that was the problem.
Engine runs smooth? Mileage is good? Everything seems to work fine except the tach? At 250,000 miles, it might just need a new tach.