P0300

[DamnItAll]

Ok here's the deal. 05 aveo 150k miles I just got it. Thirty seconds of driving, check engine light starts flashing meaning misfire. Car runs fine with plenty of power. Plug in scanner sure as **** p0300 and is only code. Look at misfire data, isnt ticking any misfires even though ses light is flashing... kinda weird if you ask me usually flashing means hard misfire... anyway so I drive it and once in a blue moon it ticks history misfires on 2 and 3. Ok sure do a tune up with new coil... problem is still there. Also when I first got car it wouldn't start cause of corrosion on crank sensor. I cleaned it and also did crank variation relearn attempting to fix issue so it starts now just misfires... anyway I'm thinking I might have a valve issue but would just like some input before I drop several hundred on parts. If that is the issue would just valves fix it or would I need a head? Will a leak down show this very intermittent misfire? Or maybe my crank sensor is stupid causing it to tick false misfires? I'm out of ideas and ways to test **** I appreciate your time thanks.

[DamnItAll]

Forgot to mention ran compression test and had 160ish on all cylinders. Car does not act like its misfiring at all.

[xintersecty]

I got a code before with the cam shaft sensor. Have you considered replacing that? Possible issue with timing belt? I would check the ground going over the the coil pack.

[DamnItAll]

Nah. Ended up doing a leak down and found some leakage out the intake valve of #3. Probably just gonna throw a whole head with valves on it to be safe. Just gonna cost me an arm.

[xintersecty]

Nah. Ended up doing a leak down and found some leakage out the intake valve of #3. Probably just gonna throw a whole head with valves on it to be safe. Just gonna cost me an arm.

That is a bummer and a lot of work. At least you know what you are doing! Hey at least you can refurbish the old head and sell it.

[avguy]

JMO, but I think it would be a mistake to do anything with the head. You said compression was 160 on all cylinders and I don't see how that could ever produce a flashing (i.e. 10%) misfire. Plus, just being off a slight bit on TDC could give the red leak down reading. If you want to hang on a much less expensive part, how about a new crank sensor? You cleaned it and the vehicle started, which would seem to prove that something was going on with it. If it's running great as you posted, then maybe the misfire being reported is just bad output from that sensor.