Not exactly sure on the technical aspect (my competence) of swapping the injector with another one...if I did that, I assume I would eventually get the same trouble code for the cylinder I swapped with (thus isolating that injector)?
I was able to verify that the #2 injector is working, but that is all.
I ran the engine briefly with the #2 injector disconnected from elec pwr. I verified voltage to the injector and injector continuity. The engine ran obviously more smoothly with power to the injector connected. I know that doesn't necessarily rule out a problem with the injector, but does rule out the #2 injector electrical circuit and functioning of the injector.
Based on some of the other possible causes you've mentioned, I'm wondering if any of those can be ruled out based on the fact that P0302 was the only malfunction code. There were no other codes or pending codes. In other words, since I had no code indicating a problem with the EGR can that be ruled out?
By the way, here's a little more info to go on: the fuel filter was changed with the timing belt at 105k (about 5k miles ago). The spark plugs have less than 20k miles on them. The #2 spark plug electrodes are whitish gray and dry.
Unfortunately, I may be nearing the end of what I have the competence and equipment to check (ie cylinder compression, fuel pressure). Other than changing the parts, can I check coil voltage or spark plug wire integrity? There is a small grayish white area on the wire, but as I previously mentioned, the #2 spark plug wire's resistance was the same as the other one.
Are injector cleaning products that are added to the gas a waste of money in your opinion? Might help? Can't hurt?