I answered in the other thread, which I will delete. This is what I said:
x046866 - The original poster was right, I believe - there is a cut-off that causes the "loping" at 1500rpm. What you want to do, is adjust the rpm when cold to below 1500rpm - say 1400rpm - that should stop the loping. Then drive the car until warm and see what the rpms are at operating temperature. If still high, adjust them back to about 700rpm in Park, using the adjustment screw Then put in drive and see what they are. If it is about 500-600 rpm, then you are fine. If lower the car might not idle evenly and may cut out. Key is to stay below 1500rpm when cold.
If you can't get rid of the problem by adjustment (for example high rpm even with screw all the way in) , then you might want to check for proper operation of the Aux Air valve - it might be sticking (you will have to remove it, soak it in a solvent and cycle it through operating temperatures by putting it in hot water). Also check the resistance of the two temperature sensors per the manual. If everything is OK, then look for other vacuum leaks. There are only a few vacuum connections on a '73.
