Is it possible for a worn out valve gasket to cause a misfire?
I drive a 2003 Honda CR-V automatic with 199,876 miles. I've been having persistent misfires with P0300, P0301, P0302 trouble codes. I went to a Honda dealer near my area and was told that it was due to spark plug from cylinder 1 causing an issue. I was recommended to replace it with original spark plugs and ignition coils. I recently replaced the original Bosch iridium spark plugs with NGK spark plugs. I didn't even have 7,000 miles with those Bosch iridium spark plugs. At the same time I replaced the ignition coils with Duralast ones from Autozone (Yes I know they are not Denso or NGK). When I took them out yesterday, I noticed that cylinder 1 was more burnt than the other cylinders, and cylinder 1 and 2 had crud on it, with cylinder 2 having the most crud on it. The Honda technician also told me that parts of the valve cover gasket is cracked I think for cylinder 1 and cylinder 2. Something like that.
After I replaced it, the check engine light came back on instantly. I was surprised to see that considering that it would take time for it to happen. I started to think about the process of installing the spark plugs. I don't think I over-tightened it because I used a torque wrench (Hopefully it wasn't faulty because I do remember having to turn it more than 13 lb-ft), and I may have applied a little too much anti-seize. Not that I put the anti-seize on the tip of the spark plug, but I did put a nice even coating of anti-seize all around the threads of the spark plug. Though I may be overthinking about this, and I know I have changed the spark plug on my car before.
I just can't help think about the worn out valve cover gasket, and it may explain why I have crud on the spark plugs. Also, I have noticed a leak under my car and I suspect that it may be due to a worn out valve cover gasket. I already had the valves adjusted I don't see a noticeable vacuum leak. I never tried a compression test or checked the fuel injectors. Whatever the problem may be, please help. Better yet, Scotty please help!
If the pictures were sent properly, you should be able to see my old spark plugs I took out. It starts from spark plug 1 from cylinder 1 showing the ground terminal first and terminal nut second, then the next spark plug shows spark plug 2 from cylinder 2 etc.