i drive a 94 ls/vtec with quite a bit of work. i just rebuilt it about 2 months ago and ever since i have a rough idle and when vtec comes on black smoke comes out the exhaust. i took it to the dyno to see if hp was the same but i lost about 18hp. i was hoping to fix it my self but not sure what to check. could my valve lash have anything to do with it? any replies is appreciated.