I worked on a 560SL with the exact same symptoms and it was the ignition control unit. The fact that it occurs at high temperatures is a clue, as they are prone to heat damage. You are using the paste to mount it?

What do you mean by a "messy" signal from the air flow sensor?

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe