[PabloN]

Pardonez moi if this topic was brought up before--it didn't show up on a quick search. Many years ago (2013) my wife and I took my year-old FR-S on a road trip to Colorado. Somewhere in South Dakota there was a section of highway with pavement stripped down to a corrugated surface. I kept up with the traffic and the engine started running real rough. I took the next offramp and then the engine ran smooth again. I opened the hood and all the visible wire connections looked ok. I began worrying it was a gremlin Toyota and Subaru had overlooked. But when we got going again I kept the speed a bit lower, and I never had that problem again.

Just last week I read how some cars have a "rough road" sensor (not ours, I think). Apparently without this sensor, vibrations from a rough road can fool the knock sensor into causing engine misfires. If the problem doesn't persist, the misfire record gets erased from the onboard diagnostics. I don't know for sure this is what happened, but at least it sounds reasonable...