High Idle at startup

I have 2000 isuzu Vehicross that has a high idle around 2000rpm at startup then it dies down to 1000rpm and then stalls. I have changed the idle control valve, fuel pressure regulator, EGR valve, both front O2 sensors, cleaned the MAF sensor. engine light is on error code is system too lean on bank 1 and bank 2 but but O2s have been replaced.

You have a vacuum leak!!!

[b]Yup! A vacuum leak somewhere on the engine.

Look for things like a leaking throttle body gasket or intake manifold gasket.