[Scruff]

Only symptoms i know of if its on its way out is that the car'll go into limp mode and not give you full boost (bout 8/9psi rather than 13ish). Along with this it might be a little jerky. I was told that it can be an intermittant thing though so it may run fine for a few weeks then muck about for a week, then randomly come back to life.

See if you can borrow one from someone whose car is working properly. Only takes 5 minutes to swap out.

If you haven't already tried it, take it out and give it a clean with some carb/brake cleaner then give it a little rub with a cotton bud. Be gentle cos they're not that strong.

While you're at it give the boost solenoid a squirt.

Hope thats of some help.