I also own a 1985 735i and I bought it with the idle going up and down, as if you were revving it up repeatedly with the accelerator. The guy i bought it from said it just needed a idle control valve, so I went and spent $109 at Autozone and installed it myself and that took care of the problem. It's simple to install too, it's right on top of the engine. Just connect two hoses and a wire harness. You might be able to get it cheaper on E-Bay if you want to go the used parts route.