If you have the air injection reactor (air pump) system still on your car, replace the one-way check valves and check to see that the diverter and atmospheric dump valves are operating and properly connected. That or you're getting air introduced into the exhaust where and/or when it shouldn't be.
On the other hand, if you're leaning out, you need to check the fuel pressure while on a WOT run.
Hope this helps.
