steady high idle

[MrBurgundy]

Working on a friends 83 320i and it's steadily idling at 2500 rpm in park or neutral, but when I put it into gear it will drop around 1000-1200 rpm. Also, there is a small vacuum leak, which I have not found yet. When I spray around the intake boot the rpm will slightly raise itself.

I don't have any experience with the m10 and its mechanical injection.

My question is, are there any failing parts that would cause such an idle? Or is this car super sensitive to vacuum leaks?

Also, I was adjusting the fuel trim, so I don't believe its a fuel issue.

Any insight would go a long way in my mission to get this car out of my life haha.

[MrBurgundy]

Solved.

The aux air valve was stuck open. I took it off and could see that it was stuck slightly open. I removed it and soaked it in wd40 for a while, but it was still stuck.

The way I diagnosed this problem was by removing the aux air valve and plugging the two hoses that lead to this valve with my fingers.

If the valve is bad and you do the finger trick, the engine speed should drop.

[MrBurgundy]

The air valve was part of the problem... So, after replacing the air valve, the car will idle okay until you hit the throttle.

Throttle is not getting stuck open, from what I can tell. Now I'm curious if the TPS could cause the idle to stay steady up around 1.5k

Would a TPS malfunction cause a problem like this?