On your hood there is a spec for lash, it would be in the same measurement as you do your spark plugs ,so it might be like 15 , the 15 is the room between your camshaft lobe and the roller part of your rocker , you should be able to slide a feeler guage with the number 15 on it with just slight resistance( remember the 15 number i just picked out of a hat i don't know what the lash should be on your car).But in order to do all this the piston and cam have to be is a specific position, engine should be hot for best results. Now the mechanic said that it doesn't matter if the valves are to tight that is b.s cause it wouldn't matter if they were to loose either. If the valves are to tight than what you are doing is opening the valve before the cam lobe , so if the valve is to tight than the valve might be open the hole time and i don't know but i don't think the engine is designed to do that. That is why it is called a four stroke and if the valve is open than why put a cam shaft and the valve in if it doesn't matter. Anyways i don't know if that is your problem but sometimes you have to back track in order to find your problem, i had to do that with my own integra because i messed something up and 6 months later it bit me in the ass.And scanners ,fuel pressure guages and every test in the book that i tried did not work , so i just thought about everything that i ever did to the car and remembered that i had a problem with the upstream o2. Hope this helps