95 Geo Prizm

Chances are your '95 already has OBDII in the ECU. I had a '95 Tercel and it was OBDII compliant, but they still had to do the old style emissions test, because 'oficially' OBDII didn't start until '97.

Good thing, since the ECU kept throwing a P401 code, and did it every third time I ran the car. When inspection day would come around, I would unplug the ECU power cable, reset the ECU and send it in for the test. Passed every time!

Oil too high? I would either check the oil to make sure there isn't fuel in the oil. If a plug wasn't firing right, the fuel could leak past the piston rings and into the crank case. Oil diluted with oil doesn't lubricate well.

Jeff

Trouble code 25 is an OBD I trouble code.

Some trouble codes are self-clearing. As for the engine running smoothly now, that means that the spark plug fouling was a symptom, not a cause. You may have a leaking valve stem seal. Watch for lots of smoke from the exhaust when starting the engine after it has sat overnight.

I could do it either way on my Tercel: I could short the Diagnostic connector under the hood and read the flashes, or we could plug into the diagnostic connector under the dash with a code reader and read the OBDII code!

Hmmm, I didn't know that any cars were set up that way.

I thought it was odd, too! I saw the "Diagnostics" connector under the hood, but when I took it to a guy who had a shop, he gets out the code reader and plugs it in under the dash! It spit out the P401 code.

Maybe because OBDII wasn't 'official', htey still included the connector under the hood just for us Ol' Timers.

True, a fouled plug, unless the center-to-case resistance is > 10 ohms should be changed out.

Keep an eye on that plug. If the source of the problem (eg oil leak) isn't cleared the plug could foul again.