Hi all. I'm new to this forum, but have owned multiple crown vics and am familiar with the 4.6L modular motor. Yesterday I bought a 1999 Navigator with the 5.4 that is having a strange engine issue. The engine starts, but dies any time it idles. If you continue to give it gas it will keep running until you let it idle. There are no codes being thrown. I read a few threads about these trucks having IAC issues. I plan to check out the IAC tonight after work, but if that doesn't fix it what other things should I check out? The previous owner stated that he thinks the intake manifold is cracked, but there is no coolant leak, which is how I've diagnosed cracked intakes in the past. Could a cracked intake cause the car to die out like it is doing? I know that on Crown Vics the intake manifolds are absolute junk. Are the intake manifolds on these 5.4s flawed too? Please point me in the right direction of things that might be the culprit of the engine constantly cutting out. Thank in advance!

 

Check the fuel pressure at the fuel rail. Smoke check the intake and all vacuum tubing with a smoke machine.

-Mike