Carina E 1.8 7AFE : tingling sound in air intake manifold

[Stevanom]

Our 1997 Carina E 1.8 with 7AFE lately had a tingling sound in the area of the intake manifold when the engine was cold.  That suddenly disappeared but now whe have the orange engine light on the dashboard and when reading it out : code 21 Oxygen sensor...  

Where is this sensor located or is it the same as the MAP sensor?

What can cause this tingling sound? (some are speaking of a certain type of valves in the intake manifold)

Would the intake manifolf of a Celica with 7AFE fit and solve this?

In the meantime we are not using the car but we do need it. (only 100.000 km)

Thanks already