Why does my 2005 toyota sienna smell like gas fumes are coming in when heat is turned on and im at a stop or idle?

Probably one of the lines going to the tank isn't tight or is broken or something, on top of the tank; or, the tank filler neck got cracked or there is a pinhole leak somewhere. Check to see if there is any gasoline stains after is has sit for a while. That would indicate a larger and more noticeable leak. If you do not see one then it may be a crack along the top somewhere are small enough like a pinhole that it is not leaving a puddle or stains anywhere. Smell = Leak somewhere.

Since you said there is no puddling then it is probably on the top somewhere so the gas does not leak out.

Ok thank you been going crazy trying to figure out so check the top then of gas tank?

You can only smell it when i have my vents on though it dont smell out side of car

it has something to do with the intake/throttle body area, I have the same issue, and have narrowed it down to these parts after changing plugs.... there are several hoses that are difficult to get to when reassembling, most likely one of those is the culprit