Help: Misfire P0125 & P0300

[alopez]

Hello Everyone,

I have a friend who recently purchased a 98 Corolla with drivability issues which we are trying to diagnose. We pulled the vehicles codes and it is throwing a P0125 insufficient temp for closed loop, and a P0300 random misfire. The vehicle idles fine and he says it does not cause any drivability issues until the vehicle is running on the road. The check engine light does not flash until the vehicle has been running for quite some time as well. Is there any direction anyone can provide in aiding me in diagnosing this vehicle? Im thinking the wires are wired in the wrong firing order or there is a timing issue.

[sam333]

Is the check engine light flashing on and off very quickly? Does the po 125 come on right after the missing? P0 125 is telling your front oxygen sensors voltage is not swinging high rich( voltage on the oxygen sensor is supposed swing rich( high voltage) lean (low voltage) back and forth. Its staying lean ( low voltage).

It can be caused by problems with the fuel system,injectors,ignition system,gas leaks on exhaust sytem,open or short in heated oxygen sensor circuit,heated oxygen sensor ( bank 1 sensor 1).

Given that you are having the Po300 code also , they are probably related( when the engine misses the oxygen sensor sees lean exhaust gases.

First do a complete tune up , with a manual.

Given its all your cylinders ,I would check your fuel pressure fuel filter and your ignition system as per the manual .