sensors

I have a 1991 s-10 blazer with a 4.3, where do I find the throttle positioning sensor and how do you check it or clean it. Also which wire on the computer it the o2 sensor input so I can see if the voltage is getting past the wire connection (which is in a hell of a spot up under the manifold) Does the o2 sensor wire go directly to the computer or does it first enter the engine compartment and then go through the fire wall?