Josh535

Hi everone, I am new to bimmersport and was after some advice on a problem i'm experiencing with my 89 535i. The idle jumps from 500rpm to 1500rpm and is also very spluttery + blowing black smoke. I spoke with Brent(hartge535) on the weekend and he told me of a few things i can check but being totally mechanically un-experienced i was after some documentation i could pass onto my mechanic. I would appreciate any help. Cheers Josh