Context: hadn't changed oil for about 4000 miles (50-50 highway-city) and had just bought supplies, father-in-law just changed spark plugs for me ten days and 800 miles prior to malfunction indicator (MIL) coming on. Also had just added Heet fuel injector cleaner/antifreeze for the first time in ownership history (some 50,000 miles).
Incident: Driving home from work, MIL comes on. Checked it at O'Reilly's today, get code P0301 or Cylinder 1 Misfire Detected. Several possible causes (base engine mechanical fault, air leaks, fuel delivery component fault, or ignition problem) but what really stuck out to me was the possibility that a spark plug was involved (i.e. ignition problem). However I had already driven it 800 miles on I-70 from MO to CO and performance seemed fine most of the way, with some sluggishness getting into CO I assumed may have been the elevation/slope acting on the not-so-powerful engine. After all the 2001 CR-V has never been that powerful and always gives me a little grief on the highway over speeds of 70-75 mph on a hill.
What do you all think? Could a spark plug cause this issue even after so many miles on the highway? Or am I better off looking elsewhere? How much can I safely drive in the city with this misfire detected?