welcome to the forum mate,

rust is something ALL cars get when not looked after........... one of the joys........

I dont have a 3.0L, but as said already, it could be going into "limp" mode

go to Supercheap and buy some MAF cleaner, and take your MAF sensor out and spray the living %^^%$# out of it - you would be amazed

there is a few threads about it (MAF = Mass Air Flow)
also look at the NADS - as that will give you some more options to look at and repair


they are a great beastie, sometimes we have to spend a heck of a lot of time tracing poor & shoddy work from previous owners to get them running right
hang in there, it will be worth the effort