The screw on the throttle body is an air bypass across the throttle plate and sets the base idle level. The bit that sticks out of the plastic boost pipe is a combined air temperature sensor/CO pot. The screw adjustment on top (under the blue cover) is the CO adjustment, but it's only for fine adjustment of the CO at idle. It's not going to fix a more serious problem (personally I would leave it alone). Check dizzy cap, leads, plugs, blue temperature sensor first.