Not to distract from the OP's original post and being a wet Sunday here thought perhaps a more positive approach is needed..
Could it be that you have a partial injector blockage think it's called "leaning" can cause increased fuel delivery having the effect of over fueling and creating higher emissions..
Possible solution could be a couple of tanks of Forte however, if it doesn't cure
the problem then could be a partial blockage of an injector filter,poor spray pattern etc. There is from what I've read, possibility of solvent insoluble particles such as sand, rust etc which additives can't dissolve.
Could be a job for a specialist..sure there are some here
