Dying, Fuel Relay buzzing, Tach wrong RPM.

I have been battling an idle control problem and finally replaced the Idle Speed Control and Air Slide Valve. After driving an hour the idle speed is much more stable but there is still an intermittent stalling problem. It always seems to have 2 symptoms when this happens.

It only dies at idle when hot and before it dies, the tachometer will show 2000 rpm at idle (like 2 times the actual engine speed) and the fuel pump relay will be clicking, sometimes so fast it’s like a buzzing sound. I can hear it, feel it and it gets warm. It usually starts up fairly easily but sometimes needs to sit but only for a minute or two. The fuel pump relay is 3 months new and I have replaced the fuel filter, plugs, distributor cap and rotor, timing chain, rails and tensioner within the last 2000 miles. Could it be related to the thermo time switch? How about the tachometer or related items? Any ideas are appreciated. My curiosity is turning to aggravation.

1985 SL500 Euro (107 with 117 motor at 99,000 miles. Has Lambda but no air pump.)