I can not give a reason , technical at least but fancy plugs suck in the 4.o change to regular Champion plugs they run the best and are the factory replacement for the vehicle. Again replace the o2 with a factory one. DO NOT run that Pass or Don't pay crap in it , that stuff actually drives up the HC and NOX , If you want to clean it out internally , one pint or ATF to a tank of gas is the best cleaner you can get. Be sure to run the entire tank empty before testing again . As for the hose not being attached that would not cause a failure other than it should have also been tagged as missing or modified ( a separate failure) as always good luck !!