So I have a 2000 4.6L V8 F150. It's got about 130,000 miles.

Sometimes if the truck is sitting out when it rains, or is just wet or humid, the engine runs really rough for a while. Seems like after it gets warmed up or dries off it runs a little better.

It seems like it idles really rough and has a loss of power. I've owned this truck a couple years. I think it started doing this maybe a year ago.

Anyone know why this is?

Does it need new plugs or something? I have no idea when/if they were last changed.

 

I'm assuming no codes so my suggestion is if you have an android phone get a BAFX bluetooth scanner and look at the numbers from the engine. Have you replaced/cleaned the MAF at all? Also when was the filter changed?

 

Could be a MAF problem or possibly #3 and #4 having water drip down on them from the area above the heater lines.

 

Check the hood seal, that where water intrusion can come from and dump just about anywhere into the engine compartment. usually b-lines for a coil.

 

I'll try cleaning the MAF. The hood seal thing is a possibility too. I am starting to think this happens more often when the truck was left outside when it rains.
It's kind of rainy today and didn't notice the issue.

 

That's correct, no codes.