Please help, m42 idling at 3500rpm

[E30 Wagen]

I won a 318is slicktop from a local auction for kinda cheap. It looks like the car has sat for years, no idea why. Engine bay looks a bit gross but not terrible. It starts okay, but it automatically idles up to over 3000rpm. There's a CEL, however, when I drove home, it would go away whenever the engine was over 3000rpm or not under load. I get a CEL everytime I start it up. Engine seemed to run pretty well otherwise, which keeps me hopeful.

I taped up all the vacuum hoses as best I could, tried a different ICV, different afm, and a new intake boot, with no difference. I can't believe a fault with any of those would cause it to idle so high, though. I tried unplugging the throttle position switch but that didn't change anything, neither did unplugging the oxygen sensor.

I tried the stomp test and got this:
blink - pause - blink - blink - pause - blink - blink - blink - blink - blink - blink
I'm pretty sure it just repeated after that. Any help with further troubleshooting ideas would be much appreciated. I have another 318is I can steal parts off of to try things.

[jntar]

I've seen throttle cables stick open before at the throttle body. Check to make sure it's fully releasing the cable.

[E30 Wagen]

But wouldn't that not matter if I unplug the throttle position switch? Or am I failing to understand what the TPS does?

I compared the good throttle to the bad one, and I can see the small top one is cracked open just a bit compared to the good one. Would that really cause it to idle at 3000? Either way I'm going to clean it and hope it works.

[Dj Buttchug]

No what he means is the actual cable is stuck holding the throttle plate open. This happens alot on m42 cars because of the way the throttle cable and adjustment nut are. The cable will split from the mount and pull out some thus holding the engine @ well past idle.

TPS tells motronic the position of the throttle plate

[bmwman91]

Wait, so when you look at the dual throttle plates, the smaller top one is partially open? It should be fully closed when the gas pedal is not being pressed. The throttle position sensor has nothing to do with it since it just tells the ECU how far open the throttle is, but the amount of incoming air will actually determine RPM and that is a function of how open the throttle is.

Take a picture of the throttle being open, maybe that will help us understand.

[E30 Wagen]

Yeah, it was definitely the throttle causing the high rpm. At first glance it looked closed but looking closer it was stuck open a bit. Unstuck it and now it idles fine! Can't believe I missed that...