95 Honda Accord Sedan, 4 cyl, 206k miles

Symptoms, may or may not be connected.

1. Tachometer shows unexplained increase in engine speed.
2. Engine stops, tach bottoms, as if the ignition is turned off. Just instant stop. This happens at idle and while driving. If while driving, it will sometimes come back to speed (the engine) and continue as normal. (Wiggling the key in the ignition switch does not reproduce or cure the problem.)
3. Several times, after the car has been parked for 1-3 hours, the engine failed to start – no response from the engine at all, as would happen if the battery were completely dead or disconnected. On another try or maybe the 3rd try (key on, key off, key on . . .) it starts as normal. (Wiggling the key in the ignition switch does not reproduce the problem.)
4. At idle, increasing engine speed from idle to 3500 rpm, there is a rough spot, like a mild (?) miss, at 2500 rpm (maybe 2400-2600).
5. When the above is not happening, the engine runs and accelerates good, no stalling or hesitancy.

I don’t have a lot of spare time for troubleshooting right now so, I’m hoping someone can help me narrow down the list of possibilities.

Thanks.

 

ECU?

 

Take the car to a shop or auto parts store and get the codes that may be stored in the diagnostic system. You didn't see if there is a check engine light, but even if not, get the codes checked anway.

The drop in power down to nearly no rpms, particularly if it presents as a bucking and jerking that impacts drivability, could be the O2 sensor (oxygen sensor). The odd surge that you called, "mild miss." could be clogged EGR valve///

Or you could even have worn out spark plugs or spark plug wires. That will cause hesitation for sure.

Lot of possibilities, but you should start with checking the codes as mentioned.

 

Thanks for the input. Car is obdI. I checked the codes. Have also had the car in the shop, which found a defective Main Relay (FI) and that the ECU had water in it. {The car had been sitting out in all weather, not being driven when we bought it - so maybe that explains that. Shop found no obvious imperfections in the seals.] The Main Relay was replaced and the ECU dried out. Car started and ran ok. Then stopped, would crank but not start previously the engine would not even crank.
The next morning it started and ran ok, not driven just idled for a while.

I embarked on some TS and checked the TDC/CLY/CKP sensors all ok, the ign coil and the ign control module, both ok.
Determined that there was no spark. Did not TS Fuel supply, but based on the odor of gas and the lack of fuel supply symptoms I am assuming for the moment the problem does not lie there.[also, from the beginning it has seemed like a power (electrical) supply problem.]

My plan now is to obtain a known good ECU to swap-in.

If no joy, the back to the shop for at least an hour of their time.
And so it goes.