The thing is the mechanical part needs to be right, before you try the "easy stuff", you need to verify that valves are adjusted correctly and/or cam timing is right, maybe check compression, etc. Basic 101 troubleshooting. A extremely loose or tight valve is never a good sign.I'm gonna check this last. Going for the easy stuff first. i think the previous owner may have dropped it once. Could that cause the chain to slip?
There's just a handful of ways the cam timing or chain can slip, none normal, rotating crankshaft backwards or counterclockwise a lot, broken/failed cam chain tensioner, very loose/stretched chain or incorrectly installed cams.
The ignition/spark timing been mechanically off is really not possible with electronic ignition, unless a safety relay is acting up or coil/igniter is bad.
The idle is adjusted with large slotted screw, 1st loosen small locking screw, adjust and lock, counterclockwise raises idle and vice-versa. Do not mess with throttle stop screw.