I have a feeling my Accord might have dirty exhaust valves - no. 4 more than the others. (It's really having quite a misfire after it warms up and when I pull the plug boot from the No. 4 cylinder, there is no difference in idle speed).

I was researching this problem and came across a similar issue with another Honda and the person ended up cleaning the exhaust valve to amend the issue.

He only indicated he removed the exhaust manifold and cleaned it with Gun Action cleaner (which apparently is good at removing carbon deposits). He didn't specify if he had to take the head off to do this, though.

Is there a way to inspect/clean the valves without disassembling the motor? (I do have a lighted snake camera device, if that helps)

 

Are you getting spark on #4? A lot of things can cause a misfire. I don't want to call you out on your diagnosis but I must say it is unlikely that there is enough carbon buildup on your valves to cause a misfire, at least one that is noticeable. You can certainly attempt cleaning the valve with said cleaner, you can get access to roughly half the valve from just removing the exhaust manifold, you will have to rotate the engine to get the valve in its full open position. It MAY be possible to rotate the valve from the exhaust port to gain access to the other side for cleaning but be very careful not to damage the valve. Removing the head would get you access to 100% of the seat, face and transition region which would be the right way to do it but is awfully time consuming for something that may not fix your problem. I'd make sure you have spark, fuel and compression in all your cylinders first then get back to us.

 

I unplugged the boot on no. 4, removed the plug, plugged it into the no.4 wire and did a quick crank with the key - definitely sparking...

 

Do a compression check next. Easier than pulling parts off.

 

Will definitely do that next...I'll keep you posted.