There needs to be a tiny bit of slack in the inner, NEVER put oil or any lubricant inside the cable, that will swell the nylon in nylon cable and make it impossible to drive smoothly.
Check that the outer adjusting nut near the throttle body has not stripped the thread.
Thats usually done by putting your foot down way too hard going past full throttle, they seldom just break from normal use or come undone as the nut is a self locking style, similar to but a cheaper form of a nylock nut.
A quick fix for that is some thread tape and a few good cable ties, that will hold the outer in place until ya can get a new one, $20 from GM, unless the outer has actually broken, whatever buy another.