spyglass

98 Honda Civic DX. The codes were accidentally cleared, but I am getting stumbles at acceleration at low speeds. It seems to be get worse with hot weather. Is this an indicator that the oxygen sensor is failing? If so, which one? I am thinking it's the one in the engine, which I believe is called the upstream oxygen sensor? Thank you.

ezone

If you think the O2 sensor is causing it to stumble, then simply unplug it. (You are right about the upstream sensor there.)
See if it still stumbles. I bet it still does.

If it still does, then keep checking elsewhere. Ignition is the usual cause of a load related misfire. Cap/rotor, wires and plugs.....and the plug holes full of oil on many of the engines.

spyglass

It did turn out to be a distributor issue. Your advice right was on target. Thank you. I think the key was it did not throw a new CEL code after the old one was cleared.