Sure, there are times where he asks for help - see Journey's End with its multi-companion operation - but most of the time, the Doctor would really prefer that you keep your grubby paws off his One True Love. Especially if your name happens to be Jamie McCrimmon. The TARDIS is held together by haphazard jiggery-pokery and luck, considering what the Doctor puts her through, and it would be considerate of you to respect that, thank you very much. He calls her Sexy" after all, and you wouldn't just stroll up to another person's wife and start prodding at her now, would you? Besides, the TARDIS doesn't like it either. Have a little respect for this great, albeit rickety machine.