Hi, just got a 99 EB with the 5.4 and It's been a marvelous truck until this morning... It starts fine, but as soon as you let off the throttle it dies (immediately) no rough idle, just dies. It was close to freezing over night, but it is in the garage. Any ideas as to what is causing this???
If it still dies after warm up, you may have a bad throttle position sensor. I hesitate to say that as this is fairly new vehicle and the TPS usually lasts several years before giving problems. Checking for stored memory error codes may give an indication as to the problem.
I had this problem. Turned out to be the Idle Air Control valve. I removed mine and ran the tests listed in the Haynes manual. The unit tested within spec, so I cleaned out the carbon with brake parts cleaner and a pipe cleaner, reinstalled and it ran fine. Regarding the tests in Haynes' manual, the IAC ohms were 11.0, the manual said the range would be between 6 and 13 ohms.
One more thing can cause the engine to start but not idle is the EGR valve stuck wide open, so if your IAC valve tests OK, check the EGR. Also, EGR valves are NOT available at AutoZone or Napa yet. Dealer only.