How can I tell if my idle speed is adjusted properly?

After doing my timing chain, belts, hoses, & valves two weekends ago, the car ran better than it has in a couple of years. After about a week, though, it developed problems with sluggish idle, to the point that it would even try to stall when idling. It ran fine otherwise. To keep it from stalling out, I'd have to press the pedal a little bit while idling. My idle adjustment key on the dash does not work; that's a different story.

After a few days, it seems that the problem is gone... which makes it really difficult to diagnose and fix.

Anyway, I don't have a tachometer.. there's a clock instead. How can I tell if my idle speed is adjusted properly? I've been using the oil pressure gauge .. but I don't know if THAT is working right, either. I guess I could just "listen to it" .. that's my next option, I guess.

Also, does anyone know the job number(s) in the service manuals for replacing the idle key on the dash? I've searched high and low in all three manuals (Engine, Chassis 1, Chassis 2) to no avail.

Thanks for any insight. Sorry that this post turned out to be more of a whine than a question...

- Nathan
'83 240D, 250,000 miles