I have a 1999 Ford F-150 with a 5.4 motor. I have had it approximately 1 1/2 years and have had the same intermitent problem since shortly after its purchase only lately it has gotten worse. Until recently everytime it rained it didn't want to start up initially and I have to attempt starting and then rev it up for a about a minute for it to stay running and then it works just fine. Recently however it has surpassed the initial issue and now when it rains the Service Engine Light comes on and it will actually stop running when I am driving. This has happened on two occasions and they were when I was either slowing down or almost stopped completely. Also then and now it runs real rough during acceleration between 30 and 60 MPH. Mind you it only occurs when it is raining or the day after a rain. Before I take it in for a what may be a costly diagnosis, does anyone know what the issue may be and if it is something I can easily repair or have repaired somewhat inexpensively at a shop? Thank you and your assistance it greatly appreciated.

 

Since it is rain related, is there a leak from the windshield getting into the computer or dropping onto the engine from some area? Have you saw anything wet that should not be.
It's a simple question but almost has to be something like that.

 

I have checked for leaks near the windshield however I have not found any so far. That is a thought I had however finding a leak anywhere sometimes is very hard. To wet to check when it is raining and usually not enough water to find a leak when it is not raining. However that question does bring me to seek it out in more detail somehow. Thank you.

 

A good starting point would be to read the codes.

That way you will know what the computer is having problems with and will eliminate a lot of speculation and guesswork.

Steve