The National Highway Traffic Safety Administration posted a document late this week launching the investigation into Toyota's Matrix and Corolla cars. It's just the latest in a recent string of quality-related issues for the Japanese automaker.

The document cited 26 complaints from drivers of 2006 model year Matrix and Corolla vehicles. Consumers "allege stalls occurring randomly while driving, including some on highways and some in intersections," the agency stated.

The new investigation is another blow to an automaker that has seen its long-held reputation for quality come under attack amid a flurry of safety-related recalls and investigations this year.

Last week, Toyota said it would recall more than 4.2 million Toyota and Lexus vehicles in the U.S. and Canada because their design increases the risk that they could suddenly accelerate out of control. In addition Toyota recalled 110,000 Tundra pickups because of a rust problem that could cause the spare tire to fall onto the road, creating a hazard for other vehicles.

Toyota has announced recalls of more than 4.8 million cars and trucks in the U.S. and Canada since January. Other than this year, Toyota's largest annual total of recalled vehicles over the past decade was 1.1 million in 2004.