What can cause bucking? Running lean, likely from low fuel, either the O2 sensor is acting up or the fuel is being starved some other way. Like mentioned, low fuel pressure or some other sort of mechanical restriction. There are a number of sensors that affect fuel flow or injector pulse duration. The O2, MAP and the TPS. The MAP in my experience usually fails full rich.
A timing problem can cause bucking, timing is mostly controlled by the TPS with input from the CPS, speed sensor and MAP.
Ignition problems can also cause bucking, a bad ignition cable can jump to a nearby spark plug cable and fire the wrong spark plug at the wrong time. Or short to ground and fire excess fuel in a cylinder from the last miss fire. Or weak spark can cause the same.
Very white plugs are a sign of a very lean motor. This can also happen from vacuum leaks, enough fuel, but too much air. Often indicated by some plugs being white while others are gray or even dark gray or black. Most of the vacuum hookups on the Renix intake are off center so a vacuum leak can affect some cylinders more than others.
More exotic causes can be bad or sticky valves, coke (soot) in the cylinders that ignites and burns causes odd ignition, and distributor indexing (initial timing). I had an XJ that had been parked for an extended period, the pressure tested good, the flow rate didn't. It finally turned out to be bad fuel, some had turned to jelly in the fuel lines. Moisture or water in the fuel has caused all sorts of ignition problems over the years (not common but it does happen), it seems more common in the early winter months.
The cam position sensor has never really given me any problems at all, though a short would affect the 5 volt sensor supply circuit. I've run for months with mine disconnected and never really noticed any difference at all in the Renix (whole different can of worms in the OBD 1, post 90 models).
Lastly, a good sensor doesn't necessarily mean it is putting out goos info, the connectors and wiring may have excessive resistance.
Sorry about wasting $60 on a new O2 sensor, but at least now you have a good spare to test with next time.
I keep a box full of junk yard sensors, sometimes it's easier just swap them out and eliminate that sensor as a possible problem. But not a good idea if you have to pay too much for the process and start buying and swapping out good sensors. Besides the fact a new sensor isn't necessarily a good sensor, I've had more than a few fail right out of the box.
One third or one quarter gas pedal is a typical dead spot for in a TPS. Though it really doesn't buck, the motor just kind of dies for an instant in my experience. I had a TPS like that in my 87.
I've run out of ideas, there are probably others I'm forgetting. Hope I haven't info overloaded you.
