My friend has a 98 with the 5.4. After driving through some mud, the next day the engine will die while idling. After revving the motor for 20-30 minutes it runs fine. I noticed there was water coming out of the exhaust behind the cat and right after the muffler. He had cat back exhaust put on about a year and a half ago. Could a leaky exhaust let water in? Would this cause it to not idle?

BoiseBob

 

If you read what you put down, you basically answered your own question.