This post is for anyone who may have the problem of their engine shutting off immediately after startup. I just fixed the problem on my 98 Expedition. It was the hose that hooks up to the intake manifold just below the Idle Air Control (IAC) valve/solenoid. Mine came loose when I "bumped" my starter & had a slight misfire. The backpressure was enough to pop the hose off the connection. I re-connected the hose and the engine fired up just as it has before. I hope this will be of some help to someone.