Problem in VTEC

i'd prob reset the ECU also won't hurt. Car could be pinging due to low oil or something else

if your car is due for a service, what happens is that once the oil leavel is low or not enough oil pressure the vtec does not engage, even if it goes ion and out of vtec, and if you where turning slightly in both opccasions it may jhave disturbed the flow of oil especially if its low

Could be a timing issue. Spark plugs possibly but more likely distributor. I dunno why it would happen more in third gear though.

i reckon it could be oil pressure. Vtec cuts in an out if oil pressure is low. Check oil level. Put an oil pressure gauge in the head and chec pressure.
Should be 60-80psi at 4500rpm