when i first bought my car i did not notice this until a week later but my engine light came on whenever i went on the highway about 65 mph. so i looked the code up and it says it's either the gas cap, or .0004 of an inch hole in my vaccum line.

when i replaced the gas cap it seemed to aid the problem for about 3-4 days then it came back on again, only this time i was going about 45 mph.

has anyone ever had this problem with their car?, if so how did you fix it?

 

Ok, well speed has nothing to really do with any of this. It just so happens when the car completes the drive cycle(self tests) you are going at that speed.

You are going to need to get the system smoke tested. What it does is send a "smoke" thru the test port and check for leaks.