Is it MPI or SPI? (there's a FAQ somewhere): rectangular grey air box or great big black roundish one?
If MPI it has 2 lambdas (either or both of which may be faulty), if SPI one. A trick which can work is to clean them with a carburettor cleaner (local motor factors). They can be swines to get out, so see if your factor has a lambda socket in stock.
In this case, your Wynns might even work, but it will take a hell of a long time to have an effect.