Blac Chyna -- Cops Impounded My $300K Ride

Tyga's baby mama has some 'splaining to do ... because Sunday in Malibu she got their Rolls-Royce Phantom impounded -- for a really dumb reason.

Law enforcement sources tell us Blac Chyna was pulled over after cops got complaints a matte black Rollie was being driven erratically ... and since there aren't too many of those $300k whips toolin' around, they quickly found Chyna and pulled her over.

That's when the real trouble began ... during the stop, cops ran BC's plates -- she was driving without a license, so they impounded the vehicle -- and will only release it to a licensed driver.