equate,
No, the e30 325ix has full time all wheel drive and there is no way to disengage it. I don't believe push button AWD/4WD was around until the early to mid nineties (please don't quote me on that). And push-button 4WD is more like AWD anyway. The reliable 4WD systems used an additional gear shift with opions like 2WD High, 4WD high, 4WD Low.
I'm only guessing at this part since I don't have much experience with 4WD vehicles, but if you were to shift a true 4WD truck like a Hum-Vee (military version since that's all I have formal experience with) into 4WD low while moving...you'd destroy the tranfer case.