raymondpowens

hey guys, having an issue ive never seen or heard of before and can NOT find ANYTHING as to what it is or how to resolve it anywhere online.

i have a 1990 civic hatchback, with the factory D15B1, DPFI engine, L3 5speed transmission swap, and the original PM9 ECU.

car has 235,000 miles on it, just did an oil change, ran PERFECTLY before the oil change, and now once it warms up, any time i put my foot on the gas, it will run fine for about 60 seconds, bog down to 1000 RPM, then rev up to 1500, and bounce back and forth between the two. doesnt matter if i press just enough to get to 1500, or if i floor it, it still roams between 1000 and 1500. if i let off the gas completely, its good for 60 seconds before it starts doing it again.

no CEL, no oil light, NOTHING on the dash to indicate anything is wrong, still runs PERFECT at an IDLE

has new injectors, relay, fuel pump, filter, fuel lines, air filter, battery, alternator, starter, plugs, wires, coil, igniter, O2 sensor, Throttle Position Sensor, MAP sensor,
P/S delete, and A/C delete.

GMC93

Is the ecm flashing any codes at all?

boibuddha

Sounds like an idle air control valve aka IACV/EACV.

I'm assuming this only happens at idle but otherwise it runs alright?

Check the ECU like GMC93 mentioned and count the flashes. Then refer to the OBD0 codes and get back to us.

If it is the IACV, it is not related to the oil change. Just a coincidence and #oldcarproblems.

It's easy enough to clean on your own, just remember to burp the cooling system as you will introduce a small amount of air to the cooling system from removing the IACV.

raymondpowens

no codes, no lights, no warnings, and it does NOT do it at an idle, the issue ONLY occurs with my foot on the gas. the only reason i have to think something is wrong is that it never happened until i did an oil change.

boibuddha

Maybe a sensor or hose connection got knocked loose while changing the oil. Check all plugs along your engine harness.

I know when I disconnected the IACV plug and started up the car with it still disconnected, it did weird stuff and I could NOT rev past something like 3k while bouncing all over the place. I reconnected the IACV then reset my ECU; the issue went away.

I'm really stretching here because an oil change should have no effect on idle.

The only things that affect air and fuel are IACV and TPS. Assuming you have the correct TPS (DPFI easily cost over $100 because they don't interchange with anything else), all I see is IACV or vacuum leak causing your problems.

All other fuel and spark related things have been replaced.

Don't mean to talk down to you but when you checked for codes, did you pull your passenger carpet back and check for flashing lights? You can't always rely on the guage cluster.

Sorry bud, good luck.