Missy Elliott -- My Lambo is Being Held Hostage!

Missy Elliot insists ... her brand new Lamborghini is being held captive by an Illinois car dealership -- after she paid handsomely for the luxury vehicle -- and now, she's suing to get her ride.

The rapper filed the lawsuit in Florida against Fox Valley Motor Cars, claiming she entered into an agreement with the dealership last year to buy a 2012 Matte White Lambo Aventador (below, in orange) for $376,000.

According to the lawsuit, Missy -- repped by Singh, Singh & Trauben -- agreed to make a down payment that included $30,000 in cash AND her 2005 Bentley (valued at $85,000). In return, Missy claims the dealership agreed to ship her the Lambo by mid 2012 ... but never did.

Missy says she contacted Fox Valley for an explanation -- and was told the terms of the deal had changed because the market value of the car had risen.

According to the lawsuit, Fox Valley refused to deliver the car for the agreed upon sale price -- and demanded way more money in exchange for the vehicle.

But Missy says that's BS -- and now, she's suing Fox Valley for possession of her Lambo, plus damages resulting from the dealership's breach of contract.

Calls to Fox Valley weren't returned.