did you check the clearances on all the valves?
code 25, Lean condition, is caused when there is excess oxygen in the exhaust stream and the ecm is unable to correct it, if everything else is OK this means it is lean, but if there is anything wrong that would cause excess oxygen, like exhaust leak or misfire this will also cause this code. really, disconnecting an injector should cause a code25 not fix it.
Proper sequence of diagnosis starts with mechanical, then ignition, then fuel system.
Misfires can be caused by mechanical things like incorrect valve clearances, valves not seating properly, valve timing, etc...
or ignition problems, plugs wires, cap , rotor, or timing.
if you get around to the fuel system, oxygen sensor with low output, low fuel pressure air leaks, poor injector spray patterns, or even if it is running so rich as to cause a misfire.
I'd start out making sure all the valve clearances are correct, check compression on all cylinders then if that is all OK proceed to the ignition system.
Don't talk about it, Just do it!