Did you pull the plug and make sure it's good and not cracked on 3? Is it misfiring at idle, cruising, wot, all of them..? I've seen 3 to 5kr on my topswap when I had a vac. Leak and she held...I would doubt that you did damage if you got off of it right away..but every motor is different...also, check the injector wiring harness for that cylinder..make sure it's not frayed and it's holding onto injector.....have you sprayed carb cleaner to find vac. Leaks???