my idle jumps from 800rpm to about 100rmp and then up again and then just dies on me!! it has no problem or hesitation at all when driving though, does anyone have any experience with this?

 

Sounds more like a vacuum leak to me. Vacuum leaks act differently on different engines, some engines would idle higher if there is enough fuel getting into the motor, others would start to idle lower.

Have you had this car for long? If you just got it, possibly the idle air screw on top of the TB(n/a) or on the BACV(Turbo) needs to be adjusted to get the idle up. Sounds like your BACV is working.

 

yeh i had the car for a lil while its a N/A, and it just started doing that within a month ago but not this bad where it just dies out, some days its fine though...or i jus keep the idle at 3000 for a minute then its fine

 

is it just on start-up, or is it a constant thing. (i.e. at a stop light)?

 

yeah at a stop light thats when it starts doing it

 

i'd say a vac leak as well..... if you haven't replaced those lines yet I woul dhighly recommend that to save further headaches in the future.