Perhaps throttle plate is stuck open - try to free with a screwdriver
crankshaft sensor going.
In hot weather my Honda Accord 2000 starts but idles rough and dies.
Manual or automatic transmission?
If the engine idles and revs up okay in neutral, it is likely the torque converter clutch lock up solenoid.
my 1988 4ws Honda prelude idles low at 600 rpm
Replace the plug wires
check your timing & up your idle a little
If the plugs, plug wires, are good then suspect a vacuum leak somewhere.
Probably an alternator.
It needs adjusted it is still engaging. just like when it is running in Neutral and you put it in first gear it idles down more so than typical of a bike doesnt it ?
No idea. But mine just started doing the same thing (91 Legend L automatic). I haven't started it in 1 1/2 to 2 weeks, and the same, idles normal for a few minutes, then begins reving between 1 and 2 k rpms like it's pulsing -- does the same in neutral. About to take it in on Tuesday... I would check your tps first
mine is doin the same thing