This latest federal investigation follows Toyota's biggest-ever recall which included 3.8 million Toyota and Lexus vehicles in the U.S.
The National Highway Transportation Safety Administration is probing 26 different customer complaints involving 387,000 2006 Toyota Corolla and Matrix passenger cars unexpectedly stalling.
The federal probe focuses on the electronic control module, which is the computer that controls many aspects engine operation. The ECM was also mentioned in a 2007 service bulletin issued by Toyota regarding harsh shifting on the same models now being investigated for stalling.
In a document published last week by NHTSA, the incidents occurred in varying driving conditions ranging from highway cruising, to accelerating through intersections.
The document also stated that in many cases the vehicles would not restart properly after stalling, and in some instances stalled again.
Toyota officials have not yet commented on the investigation.