Rough idle and injector issues

I've slowly been working out all the kinks in my 97 XJ auto. i've replaced the cap and rotor, spark plugs, the injectors with neon 703's, the map sensor, the idle air control valve, the upstream oxygen sensor, new water pump, and welded the small crack in the exhaust manifold. Unfortunately, after all this, it's still idling rough. When i unplugged injectors 3 and 4, there was no difference in idle. I tested the plugs from the harness and they were getting power. To further test it, i removed the rail, then swapped the two injectors with 1 and 2. still ran rough, and it's still on cylinders 3 and 4. so i know the injectors are fine, and i'm getting power to the plugs for the injectors, the spark plugs looked fine and the wires are fine. What the hell am i missing???
Any help is greatly appreciated

I puzzled over that thing for weeks on my 89. Do a compression test. My bet is that those cylinders have very low compression, due to special type of head gasket failure between the two cylinders.