You may still have a dodgy injector.

Air will get into the fuel lines and possibly in the fuel rail and can create all sorts of problems. You'd think it would purge itself out of the system but on occasion it needs little help.

The easiest way to do this is to loosen the flare nut at the injector end. Then crank the engine a little until you see fuel come out of the loose fitting. Once you see this tighten up the nut and start the engine again to see if this solves the problem.

It may be advisable to do this on all of the fuel lines while you're at it.

Don't do it while the engine is running as the fuel rail pressure is very high and may cause injury. You even need to be safe when you do it with the engine essentially stopped.

HTH,

Jason