You need some more air!
Pull the wiring connector off the idle air valve so that you can get your multimeter leads on the two pins. Measure the voltage at idle. If it is 4-6V, then you may have a blockage in the air tubes or the tubes may be leaking or the valve might still be flakey.
If the voltage is not in this range, the idle relay may have something wrong with it.
You can increase the idle by pulling the connector off the coolant sensor at the very rear of the right cylinder head, and bridging the two contacts in the connector with an alligator clip or piece of wire. That should bring the idle up to 750 or so.
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