No, that is a failed valve cover gasket. It’s getting into the tubes and fouling the connection. Notice the oil all around the plug.

Change the plug. Clean the bore. Clean the coil. Replace the valve cover gasket.


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No, that is a failed valve cover gasket. It’s getting into the tubes and fouling the connection. Notice the oil all around the plug.

Change the plug. Clean the bore. Clean the coil. Replace the valve cover gasket.


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Thanks for your reply. I have looked again, and I seem to see some sort of oil spots/leaks on the left side on the engine (as you open the hood, on the left side - where the serpentine belt is). Two pictures attached.

Are those also because of the valve cover gasket ?

 

Yeah, this is regular wear. This is also the valve cover gasket. The gasket covers the circumference of the cover and the spark plug holes. Once you see the leak down the spark plug holes or the outside, it’s going to leak in both areas.

I’ve had the same issue already and I replaced the gasket. Misfire at weird times. Now I got no problems since.


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I just did my gasket (OEM from Toyota) a few weeks ago for the same issue............less the engine misfire.

There are videos showing how to do it and there is a write up on this forum.

Granted it "could" also be fuel injectors. One should never keep driving with a flashing CEL

 

One should never keep driving with a flashing CEL

That's my understanding as well. If it's flashing, pull over and turn the engine off immediately.

@eurisko, you may be at the point to check your timing chain tensioner for leakage. It's just an o-ring which needs to be replaced. There's a DIY stickied to the top section of this forum showing how to do it. Also check your front crank seal for leakage, and the timing chain cover as well.

 

Have same exact issue with my 03 Corolla. Oil on spark plugs and oil leaking places. It’s definitely valve cover gasket as mentioned by others.

 

I found out that the gasket part around the 4 spark plug bores to be much more hard/brittle than the part around the edge of the valve cover gasket. It was leaking internally and very little externally.

 

At that mileage, I would change the valve cover seals and replace the spark plugs.
To check if the problem is the oil or the coil pack, clear the codes. Then you can swap the coil packs between 3 and 4 and see if the misfire moves to the #4cylinder. If so, replace the coil pack.

 

At that mileage, I would change the valve cover seals and replace the spark plugs.
To check if the problem is the oil or the coil pack, clear the codes. Then you can swap the coil packs between 3 and 4 and see if the misfire moves to the #4cylinder. If so, replace the coil pack.

Thanks for the tip, but i have a question. Let's say i clear the code, and swap the coil packs between 3 and 4. So if i understand correctly, if the coil is the problem, i would get a check engine and misfire on cylinder 4 ? (like P0304) ? In order for this to happen, do i actually need to drive the car after the coil swap, or it's enough to just turn on the engine and run in idle ? If i actually need to drive the car, then for how much time ? Asking because don't want to get stuck on the road. Thanks.

And just to make sure - cylinder 3 is the 3rd from the left as you open the hood and look at the engine, right ? (i mean the 3rd from the where the serpentine belt is).

 

I went through a P0304 issue on my corolla xrs.

Started with a missing electrode on the spark plug. The sucker just disappeared on me. Moved the plug from 4 to 1 to verify the misfire would follow. Not only did it follow, the p0304 remained.

Replaced the plugs and got the correct one from my OM. It was fine for a month, then it returned. Redid my valve cover gasket and spark plug tube seals. Also replaced my coil packs. It ran fine for another month, then the day of the accident it drove horribly. It was totalled and never did see the end.

 

I went through a P0304 issue on my corolla xrs.

Started with a missing electrode on the spark plug. The sucker just disappeared on me. Moved the plug from 4 to 1 to verify the misfire would follow. Not only did it follow, the p0304 remained.

Replaced the plugs and got the correct one from my OM. It was fine for a month, then it returned. Redid my valve cover gasket and spark plug tube seals. Also replaced my coil packs. It ran fine for another month, then the day of the accident it drove horribly. It was totalled and never did see the end.

Maybe your car committed suicide.

 

You could move the fuel injector to another cylinder and see if the misfire moves with the misfire. ie move the fuel injector to cylinder #1 and see if you get a P0301 instead. You can also ohm the injector or check if it is firing.

It is probably the coil or plug but you never know. The gasket needs replaced anyway if you intend to keep the car.

 

Update. So i have bought and replaced the valve cover gasket - cleaned everything inside, cleaned the coils and replaced the spark plugs. By the way, the existing gasket was pretty "dry" and not flexible at all - it broke as i was pulling it out.

In the same time, i have switched the coil 3 (where the misfire was in the first place) with coil 4 and put everything back together.

I started the car, and immediately noticed the engine is running rough at idle/shaking - exactly the same thing as it was in the first place. Did a tour around the block - no check engine at all, just engine running rough/shaking. Pressed the accelerator and as soon as i went over 30 km/h - again, the blinking check engine. Stopped the car and scanned it - now showing P0304, misfire in 4th cylinder.

So should i understand that this is a clear indication of the fact that the issue is coil 3 - because as soon as i put coil 3 on the 4th cylinder, the code changed from P0303 to P0304 ? So replacing the respective defective coil should solve the problem ?

Thanks

 

So should i understand that this is a clear indication of the fact that the issue is coil 3 - because as soon as i put coil 3 on the 4th cylinder, the code changed from P0303 to P0304 ? So replacing the respective defective coil should solve the problem ?

Makes sense to me. I recommend only a Denso COP (Coil On Plug). There are fake Denso products online, so be careful.

 

Yes!

 

I have replaced the bad coil with a good one, and the problem is solved. No more shaking at start, check engine cleared itself, car drives normally. Thanks everyone.

 

I have same problem PO 0302 TOYOTA COROLLA 2005 CE-232 000 ML. how to fix misfire cylinder 2 ?