The combination of snarky Robert Downey Jr. and funny guy Zach Galifianakis sounded too good to be true.

In “Due Date,” the follow-up from “The Hangover” and “Old School” director Todd Phillips, it is too good to be true.

“Due Date,” Phillips’ intermediary effort between “Hangover” films, feels like a film with a serious identity crisis — one that feels like an uncomfortable hybrid between “Tommy Boy” and “Rush Hour.”

The film picks up with short-tempered Peter Highman (Downey, Jr.) looking to catch a flight out of Atlanta to return to his wife in Los Angeles, who is soon due to deliver their first child. After an incident on the plane puts Highman on a no-fly list, he and Ethan Tremblay (Galifianakis), who’s heading to Hollywood to pursue an acting career, must partner up to get back to California before Highman’s child is delivered.

The hijinks that ensue are cheap and childish, not unlike Phillips’ “Hangover.” Rampant marijuana use and an awkward masturbating scene, which might be funny in other contexts, fail to come across as anything more than humor aimed at the least-common denominator.

Don’t get me wrong, that kind of humor can be OK. In the case of “Due Date,” however, the film can never pick what it wants to be. Instead it tries to straddle a line between comedy and seriousness.

Even the usually witty and testy Downey never gets a chance to play to his strengths and is instead pushed into the background behind Galifianakis. Not unlike “The Hangover,” Galifianakis steals the show, though unfortunately, he’s still yet to match the quality of his “Between Two Ferns” Web show on film.

In the end, “Due Date” suffers from the fact that it never really finds its footing and uncomfortably walks the line between immature comedy and corny buddy flick.

That’s not to say the film doesn’t have its funny parts, but the flick never finds much consistency. Instead it segues far too often from funny to sentimental.

“Due Date” is due in theaters Friday.