I'm 19 and have manic depression, as do many extraverted intuitives, and spent almost a year cycling continually between dehydrated-from-the-crying depression and rob-a-bank mania. You can imagine how little of value got done in that time; it's thrown off my college education (though I plan to go back in the fall) and disturbed my relationship with my parents. It's my reading that many ENTPs become dependent or overconfident with their Ne and allow it to drag them into some tight spots. The cure, I'm told, is bolstering the auxiliary function in ENTP, Thinking, to sculpt my Ne- which is on permanent hypomanic overdrive, even for an ENTP- into a superior perceptual system undistorted by intuitive skimming over the details and hoping it all works out.
Now, no one's saying my Ti is in some way deficient, but it's obviously no match for my manic Ne, and that is a serious problem. How can I sharpen my Ti, and how should I apply it to my Ne?
I would suspect that Ne will always be your "default mode". That will always be a somewhat more comfortable and natural place for you than Ti. For me, as an INTP, it's the opposite. I love using Ne, but it's just not as smooth or as easy for me as Ti. In the right company it's very smooth. But, around a group of mostly sensors, it's not always easy for me to use. I could stay in Ti all day long, but I have times where I need an Ne release. I try to take advantage of those times and put it to use! I find a useful outlet for it - hopefully something that is going to help Ti along - help the plans of Ti move forward if you will.
I have business plans and ideas that I've hashed out over and over again - on paper, in my head, through research, etc, etc. If I stay in Ti, those plans don't move forward - they just stay in my head or on paper. So, when I get a burst of Ne, I try to use it in the same arena. Let's say that I want to go talk to an acquaintance at his place of business in order for him to show me his equipment and the operations of his business so that I can learn more about my own plans. I may not get a big Ne urge for another week. I'll stay in Ti mode for that week. But then one day I'll get this Ne urge. I want to get out of the house and be an extrovert. Instead of going and doing something that is unrelated to my goals, I will use the Ne opportunity and go see this guy at his business. I'll be goofing around, asking questions, being kind of funny and outgoing (yeehaw, look at me, I'm a big charming, extrovert for all of about 45 minutes).
The point is that I try to recognize when my body (or brain) naturally wants to operate in Ti or Ne. I can tell the difference. When it's Ne, I know that it may not last for a long time, so I better go make use of it while I can.
Perhaps the ENTP can learn to do this same thing, but in reverse. When you have a desire to operate in Ti - when it sounds like fun and when you want to do it, make use of that time and go at it with full effort. Dive in! Ne will be back soon enough and you shouldn't get frustrated with that. That's who you are. Let it be what it is. Just allow the Ti bursts to be effective ones and to coincide with what whatever projects that Ne is currently working on.