Such as with the browning m2's on the P-51. Even today with the weapon used on the ground, jams seem very common. I'd imagine that up in the air doing combat maneuvers jams were commonplace. If so, could the pilot do anything about it? Were they mostly caused by heat or vibration? How long would a gun typically work in a combat mission before jamming?
Yes. Many of the autocannons used on WW2 aircraft were new designs and had terrible reputations for jamming. For example, the Russian Vya-23 fired ammunition which was a bit too powerful for it's mechanism to handle and suffered stoppages with increasing frequency as it damaged itself when fired and the American M1 had a firing pin which sometimes failed to hit the primer hard enough. It seems that almost every combatant in the war had similar issues.
Some planes had devices which could be used to re-cock a jammed gun, but they were often rather heavy so most aircraft didn't use them. The common solution was to simply carry on with one gun not working; the fact that most fighters had several weapons meant that they could function with only some of them, although this wasn't ideal, both because of the loss in firepower and the difficulty of controlling a plane with more guns firing from one side than the other.