True, however the stock gas cap does have a vacuum relief valve so even if all the other stuff isn't working that shouldn't happen. Aftermarket gas cap by any chance ?

 

Or a failed vent.....

 

It's a stock cap, I have another one around here I can try that is aftermarket. I tried that with the last truck. I'm thinking now the issues are opposite though.

This truck must have a leak. I can't think of anything else. Probably time to just change all the lines out.

Any reason not to just use sprinkler hose? Because I have plenty of that. Is there a particular line I'm after that I can grab at a hardware store or do I need evap system specific hoses you think

 

Need lines that can tolerate gas fumes. Parts store should have it available in all different sizes. And it (used to be) cheap.

 

I don't know about other yr. models but my '01 1500 has 1 hose at canister that has different sizes at each end, 2 bends (looks like [ sideways). Couldn't find one of those so I used a reducing coupler (?) same size on each end as hose, clamps, & new fuel-rated hoses of greater length to make a loop since 90° bends couldn't be made.

Sample reducer. One with 90° bend might be available, IDK.

 

It was definitely a leak..

I replaced the hose at the end of the hard line going from sensor under the hood to metal nipple coming out of air intake. The hard line wraps around the back of the motor and ends in a little 2 inch hose that goes from line to metal nipple.

The two rubber splitters - one for the sensor under hood and one for the back of the carbon canister. Pretty used up probably worth replacing.

Last culprit was the bigger line coming from that breather **** (?) To the air filter box.. was cracked at the end. Not sure if that is connected to the same vacuum/ if there even are separate vacuums

The problem seems to be fixed. Not whistling when I let go of the accelerator/ doesn't idle down and act like its going to die when sitting still.

Pretty simple fix! Was thinking backwards because my last truck had the opposite issue, was clogged. Best way to do this would be to use some leak test and have a spool of fuel hose/ Because from what I saw at parts store youre gonna pay $4 for a foot and a half. No need to add a bunch of connections/ waste more money.

Thanks fellas

 

Good idea probably easier than tracking down specific reducers/ makes it easier to repair in future