This is on my 90 740Ti that I put an L-block B230ft into last year.

It had a high idle since I swapped the engine. I had been squeezing vacuum lines, and the one running to the oil trap lowered the idle when squeezed.
I checked everything else.... except the throttle body and throttle plate adjustment.

I took it to a mechanic I know, and he looked around for vacuum leaks just like I did (thought he used brake cleaner where I used carb cleaner) and squeezing lines.

Finally, he shortened the rod connecting the throttle plate and throttle reel/spool and bent the tab for the idle stop up(shortening the screw by backing it out would have done the same thing.


Anyway, the idle has been better - around 800, AC and in-gear idle adjust work, though it went back up when in park after freeway driving. I shut it off and restarted and the idle was lower again.

Long story short, the fact that squeezing the vacuum line from the top of the oil trap to the manifold lowers the idle seems to be a red herring. It happens regardless of idle speed - squeezing the line always reduces the engine speed.

Happy bricking!