Lexus RX engine mount issue

Engine mount, huh? I had something similar with my RX. Uneven idling can be a real pain. Did you check for any unusual vibrations? Could be related to the transmission mount as well. Is the rubber mount showing any obvious signs of wear or cracking?

Vibrations are minimal, but present. Cracks aren't visible. Could a bad plug really cause the error code?

Yeah, a faulty connection can definitely throw off the sensor readings and trigger the error. Given it's idling rough and you've got that error, I'd say it's worth getting it checked professionally. My issue turned out to be a partially disconnected wire to the mount sensor.

Thanks. The plug was indeed the culprit. Repair cost was 95€. Appreciate the help.