Weird Idle

[EWAustin]

I think I know what the problem is here, I just want to make sure that it makes sense before I go tear my baby apart.

OK, my '87 325is will idle at either 600rpm or 2000rpm. Nowhere inbetween.

When I raise the idle screw, it goes up to 2000, and when I lower it, it goes down to 600. It won't go anywhere inbetween.

So, what I'm thinking is that the throttle position sensor is out of adjustment, so that when I try to raise the idle, it takes the TPS off of the "throttle closed" switch and raises it up to 2000rpm. So, if I adjust the TPS, and then turn the idle up a little it should idle closer to 750 or so. Right?

I would just leave it at 600, but my car burns a lot of oil (rebuild soon) and as a result idles with a terrible lope at 600, and almost no power just off of idle.

Does this make sens to anyone else?

[AlpineIS]

It is pretty easy to check if your TPS is out of adjustment so why don't you start there? You should hear an audible click when you move the throttle plate arm (if you can call it that...sure there is a correct word but can't think of it right now) back and forth. If you don't hear it then it is out of adjustment. Period.

The idle adjustment screw should never be tampered with. When you move the screw you are actually moving the position of the throttle plate. It should be in the closed position (flush with the throttle body). Of course, you can't see its position unless you remove the boot.

Make sure your IACV is working properly and check your TPS for proper adjustment.

[EWAustin]

I already replaced the IACV with a known good one. Thinking that was the reason the car idled at 2000.

Then I found the idle screw, so I turned that down. Low and behold, it adjusted the idle.

OK, just checked, yes, I can hear the click when I turn the throttle cam. But, I think that the click is in the wrong place because the idle screw isn't backed out completely.

OT: Why did BMW put an idle screw on the throttle body if it's not for adjusting the idle?