truck was kinda running a little rough so i decided to see put some fuel injection cleaner in the tank. well anyway when i opened the gas cap up you could hear air sucking in. before i put the cleaner in i tried driving the expy to see how it ran and it ran fine. could the cap need to be replaced? or was it just some luck that it ran fine

 

Your gas cap is suppose to make a seal, so I think it was doing it's job. I notice the sucking sound also from time to time. I use a good injector cleaner on a regular basis just to keep them clean as a preventative maintenance measure. Your rough idle could be lots of things.

 

Bought my 2000 EB new in Jan 2000 and put a locking gas cap on it that month; this Spring (seven years later), I had to replace the cap with a new locking cap from Ford because the locking tabs had become worn out and it wouldn't seat or close all the way after every fill up. Sometimes it would seat, but only after gently guiding it to a part of the tabs that barely caught it. At first, I thought it was the filler neck tabs, but those are metal and my parts guy at Ford told me to relook at it or bring in the cap, which I did, and upon comparison, we found the plastic tabs on the cap were worn way down, so I replaced it on the spot. Problem solved. Good thing it wasn't the filler neck, as that part was expensive. Anyway, check the cap, even if it isn't a locking version, the regular version might be worn. You don't want to mess with a cap that doesn't lock tight and provide that seal, the truck won't run right.

As also mentioned above, the rough idle could be a lot of things. In my case, I have to clean the throttle body and throttle plate every year as it seems to accumulate gunk at the bottom of the area where the plate touches the air inlet tube; that usually smoothes out the idle a bit. Lots of other things to consider though. Hope this helps.

 

i ended up cleaning the throttle body up and also replaced the pcv and the expy runs better.