CODE 26 - Fuel Measuring Divce Rich

1989 Toyota Camry
check engine code 26 - Fuel Device Failure (RICH)

I replaced catalytic converter about a year ago
I replaced oxigen sensor about two months ago
I replace EGR valve & sensor two months ago

Failed emmission test (before the check engine came on..) on HC & CO

Is the TOO RICH error enough to cause the emmission failure (Gross Poluter)

Is the Measuring device adjustable? Where is it and how?
Is it a sensor that needs replacing? Where is it?
What is the sensor found below the oxigen sensor on the exhaust manifold?

Many Thanks & Best Regards