I have been hearing too many horror stories about breaking the idle speed adjusting screw and/or lock nut.

This is what I have to say. These two metal parts are usually stuck so tight together that they are almost like welded. This happens due to many reasons,
1. Over tightening during previous adjustment.
2. no adjustment done for longest time, leading to a JAM
3.Corrosion

This is what I do,
Nicely spray that nut and screw with WD-40, Liquid wrench or something similar( Everyone has their own choice). Then I wrap a small piece of cotton cloth around the base of the "lock-nut and screw" assembly. Then I spray the wd-40 etc. again on that cloth till its soaking in the WD-40. Leave it overnight.
Next day, remove the cloth, then I use a small size deep tube socket and slide it over the screw until it rests on the lock nut( It should be about 2-3 size smaller than the lock nut size). Now I gently tap I say it again GENTLY tap on that socket with a small pliers for about 1-2 minutes and spray it at the base again if necessary. REMEMBER GENTLY
Then try to loosen the check nut the usual way, but instead of loosening it, I try to slightly tighten it by turning the checknut clock wise. JUST A TINY BIT. DONT FORCE IT IF DOES NOT TURN.
All you do by this is break the bond between the check nut and the pump body. Then I resume loosening the check nut, and 95% of the time it just starts loosening easily.
Once the check nut is loose enough, next step is to loosen it from the screw. This may need a little force on the screw, but at least you will not break the whole thing. this works for me all the time and I have had 3-4 friends who had problem loosening that lock nut come to me and thank me.

Now before I do the final tightening after the idle speed adjustment, I apply a little antisieze paste on the bottom of the lock nut. this way your future adjustment will be easy.

I know this is too much to get a lock nut loose but I rather be safe 'cose the pump is too expensive.

This works for me.

MVK

__________________
One penny saved is three penny earned.

1985 300D Turbo 179,000miles