How do you figure out where a leak is in the air intake hose for your engine?

What is your question?

My car has had the check engine light on for 4 years! Every time I take it in it's the same thing the air intake has an issue. I have tired to have this fixed over and over in the last few years. The last time I had it looked at they told me there was a leak in the hose but they can't find it!