You proabably have a leak or a disconnected hose in your vaccuum system. Buy yourself a vaccuum pump with a guage and start checking, working from the engine back. The lumpy idle when cold could be any number of things from a bad fuel distributor to a bad enrichment valve. You may need a new steering box (very expensive), or an adjustment (expensive).
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