For those of us who are too absent minded, can you post the meaning of the various codes?

OVP is not the culprit. The OVP powers the ECU, and the ECU controls everything on the engine. If the OVP fails, the engine doesn't run.

The throttle actuator seems unlikely to me. I don't see how idle quality would be affected by cold vs. warm engine if there are problems with the throttle actuator.

I had the opposite problem with this engine - lumpy idle when warm. It turned out to be the O2 sensor. The engine ran fine when in open loop - before the O2 sensor was being read. Once the ECU switched to closed loop, then the bad idle began.

How long after a cold start does it run smoothly, before the lumpy idle begins - 1 minute? 5 minutes?