What started as a random misfire eventually narrowed down to a specific cylinder on my car. From there it was easy to diagnose what was going on, but I have my own ODBII reader too. (Ended up being burnt exhaust valve.) Just sharing my experience.

But as far as being the most likely cause? I read a lot of people saying the same, "coils or plugs." Seems like a cheap answer, but again I'm no expert. You can test your coils and plugs if you have the time. Good place to start.

Anyone else?

-Rand

 

Cleared the code and several weeks went by without the check engine light coming back on. The check engine light came back on yesterday. Car runs perfect regardless of whether or not the check engine light is on.

 

Pull some plugs and see how they look.

 

Update:

Replaced the plugs a couple months back. Noticed that the #3 plug had more soot on it than the other three plugs. It was a light (whitish) colored soot. After I replaced the plugs, I cleared the P0300 code. A few weeks ago, the check engine light came on again. This time the code read P0303. I switched the #3 and #4 ignition coils and once again cleared the code. If the check engine light does come on again, I'm hoping that it'll be a P0304 (meaning it was the ignition coil).

 

Well on your way to diagnosing the issue.

BTW... Do you ever get the flashing CEL on top of the solid?

-Randy

 

Well on your way to diagnosing the issue.

BTW... Do you ever get the flashing CEL on top of the solid?

-Randy

A "flashing CEL", would that be on the code scanner? If so, I don't think it's flashing. If it was, I didn't notice. What would a flashing CEL indicate?

 

clean the MAF and try a different brand of fuel. i got some cheap gas that caused misfire codes.

 

The Check Engine Light should flash whenever a misfire condition is occuring.

 

LOL, my brain must've been chilled from the cold temps here yesterday because it took me until this morning to realize that CEL means Check Engine Light.

Anyway, no the check engine light never flashed. It came on, but once it came on, it stayed on without flashing.

 

i have a 1998 toyota Corolla and i had miss firing on my car turns out i had a blown valve cover gasket and Oil was getting on the Spark Plugs but my Check Engine Light flashed at me when it was miss firing

Aaron

 

Have the same code with code for lean on the o2 sensor. Any ideas ?

 

BUmp this thread... Trying to diagnose my mother's issues. 2000 corolla 160K. runs great, 30K on the odo. She's had all the routing/recommended maintenance. Has thrown p0300, p0302, and p0171. If I clear it, usually will get p0300, p0300 + p0302, or p0300 + p0302 + p0171.

I changed the plugs and will wait to see if it pops up again. If the p0302 comes up, I will switch the coi packs. There was some oil around the coils in a couple of the tubes, so the valve cover gasket needs to be done. On the 2nd hole from the left (is this #2?) there was oil around the plug threads.

thx!

 

Hijack this thread... Trying to diagnose my mother's issues.

Fixed that for you.

You should start a new thread rather than hijack this one.

 

i have a 1 week used x2 coil packs, 4 1 week used wirres(1 set) for sale if needed

 

2002 Corolla with 79k miles. Check engine light came on today. Car runs great otherwise. Took it to Advance Auto Parts and thier OBD II code scanner displayed: P0300 - "".

I know it's impossible to say exactly what this might be, but does anyone know if there is a "most likely" cause for this code?

The parts store said if could be either an ignition coil / pack, or, spark plug wires, or plugs (in other words, something ignition related). They're leaning torwards the problem being the ignition coil / pack, but admit they don't know for sure.

Thanks.

BRAD CHECK YOUR FUEL INJECTORS AND YOUR OIL, I HAD A SIMILAR PROBLEM AND MY GAS WAS MIXING WITH MY OIL AND IT HAD ME PUTING OIL EVERY WEEK BECAUSE IT WOULD JUST FINISH OFF. I THINK THE PROBLEM IS IN YOUR INJECTORS.

 

how does your gas mix with your oil and consume your oil i dont get that , its like a 2 stroke ?

 

PCV system