I have a 97 f150 4.6 . When I remove the gas cap there is a loud rush of air.
Is this normal? When I took the gas cap off when then engine was running the idle bounced up and down and the engine almost died. Then the idle smoothed out. Thanks

Budman

 

That is most likely due to the gas fumes expanding in your tank due to heat from the ambient air temperature and/or sun . The same thing will happen if you set a sealed gas can out in the sun, then open it up later. This is normal.

 

Yep its normal. On one of my tanks caps it even says "Wait till hissing stops to fully open".

 

Thanks for the info.

Budman

 

Mine does that stumbling crap when I open the tank too. Expecially if I've driven it hard for a while.