It could be any number of things. could be a leaky plug wire or something like that too. Either way, if you can pick it up cheap, and it has a nice body/interior, go for it!
'86 325es (TURTL3): PJ peetsa hawler
'87 535is (BADWATER): almost done... really.
'86 325e (GRN HLL): DD/show/rocket
'04 x3 3.0i: Wife's Bimmer (manual, woot!) My BMW Blog