richard:

most obvious possibility is problem on high tension side of ignition, such
as mositure and/or carbon tracks in distributor cap, arcing between spark
plug wires and ground (might see sparks outright, or glow around wires, at
night), or, even if not root cause, fouled plugs.

O2 sensor very unlikely here, and it can be temporarily disconnected in
any case to eliminate possibility. ditto temp sensor. O2 sensor and,
though to a much lesser extent, temp sensor, are high impedence, low
current devices, so in this context a little contact resistance is
irrelevant.

dan