'American Idol' Contestant David Oliver Willis Arrested For LSD Possession

David Oliver Willis, who repeatedly appeared on "American Idol," has been arrested, after police found LSD in his car ... TMZ has learned.

According to docs obtained by TMZ ... David was pulled over last Friday in Lake County Florida for a malfunctioning headlight.

The officer says they could smell marijuana billowing from the car and proceeded to search the vehicle. Cops say they found a grinder and baggies containing several small squares of paper that tested positive for LSD.

Officers say David admitted to smoking weed with a friend prior to driving ... but claimed the LSD did not belong to him.

Because he was the only person in the vehicle during the stop, officers arrested Willis and booked him for possession of a controlled substance (LSD) ... a third-degree felony. He's due back in court next month.

As you might recall, David has had a long run with "American Idol." He appeared on season 12, season 13, and he came back for season 14.