I need a little help folks. I have a 99 Concorde that has an intermittent #4 cyl. misfire with low compression. the engine has 51k miles on it. I've had it in three shops but the problem is still happening. Ive had the head gasket,spark plugs & injector replaced and the coils moved around to rule out the coil. Once i disconnect the battery to clear the code it runs fine for the day then chk eng comes back with p304 code. What we cant figure out is why it's intermittent? I've been told bad rings? Could it be a sticky or worn valve? Maybe, but why isn't all the time? Why does the problem temporarily go away when I disconnect the battery? It doesn't seem to make a difference if the engine is hot or cold. Could it be the cam sensor? Why the compression issue?

Thank you