Jeep Repair: Check engine light

Question
I own a 2000 Jeep Wrangler Sport 4.0iL 6 cylinder jeep. For a straight year I'm getting misfire codes multiple cylinders and the check engine light. This occurs at 2900 rpm and/or at 60 mph. My mechanic has replaced the ignition coil rail assembly, installed OEM plugs, spark plug boots replaced. Cam sensor, Crank sensor, cleaned throttle body. The mechanic has also connected water to a vacuum line to remove deposits from backs of the valve(it helped for a month). The engine in the current state runs strong, no sputtering nor stalling. I live in California and it will not pass emissions with engine light on. The engine does not pollute at all. What could be my issue?  I Have thrown money at this for months!

Answer
The tech was in the right area with the water  but  not the right stuff  the dealer has stuff just for that and a TSB for this jeep   is a combustion chamber cleaner  that u can do yourself if you want.  Read teh TSB 0900303 for the info and stuff needed.