The hidden screw is tuned using a special tool. Can buy from tool shops.

Tuning an engine depends on purpose of tuning, mods done, advance setting and engine condition. No magical bullet. That's why experienced mechanics do it better.

Ok. Your case, from my limited understanding and experience, the reason they ask you to go back to stock intake is like this. You can correct me if I am wrong. The problem with cold air intakes is that you have a tendency to cool the intake manifold too much. Petrol does not burn in liquid form. It burns in vapour form, that means gas form. That's why some people call it gasoline. If you look at you manifold, there is a water manifold. That is to warm it up so that the petrol can evaporate. When you put the CAI, you cool it so much that the mixture cannot evaporate in time. If you notice, pick up is fine, in lower gears also actually ok. Only top speed runs semput a bit. Original intake gives it some warmth. If it's too cold, there is a pipe to draw warm air from the exhaust manifold. That's also why older NA F1 engines have the injectors before the throttle body not before the valves like our engines.

Another possibility is that there is not enough swirl. Mixing not enough

Sorry if too long.

This post has been edited by sakaic: Nov 20 2016, 10:40 PM