92 SC, overheated, replaced water pump, had heads resurfaced, I reassembled, can't get smooth idle since, sometimes stalls when put in reverse, but runs well otherwise. New wires, new Motorcraft platinum plugs gapped carefully, new Motorcraft IAC, new O2 sensors (due to code). No check engine light, no codes left. IC tubes sealed carefully, Vacum about 17 or 18 at idle per dash gauge. Great acceleration and boost. Blew compressed air into MAF and idle did change, appears to be working. Idle speed about 750 rpm. New fuel filter, running out of things to check, could it be vacum leak, checked all fittings and clamped that I could see and reach. Thinking of doing the test for leaks, where you inject air into boost gauge nipple to check all vacum, fuel ingector and intake manifold seal. New air cleaner. Dealer could find nothing. What else is there to check, great car, about to get painted, need it to idle smooth..please help. 