Low Idle Issue

[Pasta_Primavera_]

Hey guys!
So I recently acquired a 1991 318is with an M20 swap and it came to my attention that she idles around 500-600rpms. Now I was thinking thats a bit low and that she should be at like 700-800rpms right? My father tweaked the throttle cable and got her to 800ish rpms but then after driving around was back around the 500-600 range, Was wondering what my next step would be to fix this problem?
Thanks!

[EatsHondas]

Adjust the set screw on the throttle body.

EDIT: Remove the ICV and spray the valve inside liberally with carb cleaner or equivalent. If that doesn't help anything, download yourself a copy of the E30 Bentley manual and start troubleshooting. The instructions are well laid out and very easy to follow.

[Pasta_Primavera_]

We did... to only find that it went back to the 500-600 range. I could adjust the screw more but i feel like the idle is too high like around 900-1000

[95BMWIC]

The factory set throttle adjusting screw is not used to adjust idle speed. Its only function is to provide a mechanical stop for the linkage to prevent damage to the plate and housing..

The gap should be about .0015 in between the plate and inside the housing.

[95BMWIC]

Engine idle speed is controlled by an electronic idle stabilization system. I believe on the 1991 318 model, it is controlled by the Motronic 1.3 CPU. Idle speed and ignition timing are electronically controlled and are not adjustable. Idle mixture is also not adjustable - all done by the computer.

The electronic systems take different inputs(engine temp, air temp etc.) to adjust the idle speed. Incorrect Idle is usually caused by a faulty idle system.

Idle speed also depend on year and model - I believe the 1991 318 would be around 700-800 like you stated.

I would check the different components in the system to see if they are within spec.