7.4 had leaking manifold gaskets, so I replaced upper and lower. All was well. Then 500 miles later developed a persistent fast idle and vacuum leak. Turned out to be a loose lower intake manifold bolt. (Oops) When diagnosing the fast idle problem, I went to clean IAC and it came apart, so I replaced it with one from Autozone. Now the truck idles great and runs well. Problem is when first started it runs for a second and quits. Then when restarted it keeps running. But when first started it always dies. Any suggestions?