hi, welcome to the bord.
NOx is caused by high combustion temperatures. The EGR reduces the combustion temperature by mixing inert gasses into the air/fuel mix.
retarding the timing will decrease the NOx. You may want to even retard it more than spec by a couple degrees or more. Then after inspection, put it right on spec.
Also fill up with premium. High octane burns slower and should help too. (Less chance of detonation)
Maybe try one step colder spark plugs too. This reduces the chances of a hot center electrode causing pre-ignition.
A lean fuel mixture also burns hotter and may increase NOx. If one injector is spraying lean, that could cause it to burn hotter in that cylinder.
If all else fails, weld in a second universal catalytic converter (in series, not parallel).
(taken from
http://answers.yahoo.com/question/in...4113417AA6uoEz
best of luck