Firstfives.org

When I brought my 'new' one home, '80 528i aka Silver, the idle was at 600-800 rpm. Fine for me. Now it has slowly crept up to 1100 rpm after a warm up. I changed the plugs, but I didn't adjust the valves. nothing else has been changed. I got a new battery. That's it as far as the engine goes. Oh, new belts. Just remembered, the idle was down to 400 rpm so I adjusted to 800 rpm using the idler adjuster not the distributor.
What could this mean? Possible vacum leak? Thanx In Advance,,,,,Greg

If you adjusted the big brass screw in the throttle body out, counter clockwise, you let more air in the mix to increase the idle from 400 to 800.

Vacuum leaks and aux air valves do the same thing, the aux air closing as the engine warms up.

Let the engine get to normal temperature and use the throttle body screw in/out to set the idle to 800.

If that doesn't work, perfection is in reading, doing the throttle body tune up, timing FAQ and vacuum leaks check.