You either have a vacuum leak somewhere, or a tear or leak in the idle air valve's plumbing, or a problem with the warm-up air valve. One or more than one is allowing additional air into the system, outside of the idle air valve.

Check the rubber hoses very carefully, and try tapping the warm-up valve since it may be stuck.

__________________
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