usatoday.com | Just when Toyota thought it was getting hold of its recall nightmare, it is now trying to figure out how to fix computer flaws in up to 1.2 million Toyota Corolla and Matrix models that can cause engines to stall, the Detroit Free Press is reporting.

But Toyota has told federal auto safety regulators it doesn't think the problem "an unreasonable risk" to safety. Drive On guesses that's because these ones have engines that won't stay running, rather than engines that run out of control, the subject of unwanted-acceleration recalls.

So far, the Corolla problem in 2005 to 2007 models is not -- repeat, not -- at the recall stage yet. But this is another tough break for the automaker. Here why:

For one, the problem is in the car's computer, the electronic control module or ECM. That's the unit that Toyota insists is not at fault for unintended acceleration. Furthermore, the Corolla is already the subject of a formal investigation into another unrelated issue -- steering defects. Corolla is Toyota's second best selling model behind the Camry in the U.S. It is also included in the sticky pedal recalls.

The National Highway Traffic Safety Administration opened a probe last November into 26 complaints of engines stalling in 2006 Corolla and Matrix models, the Free Press' Justin Hyde reports. Since then, the number of complaints has mushroomed to 76. Several owners said the problem happened without warning. Sometimes the engine was hard to restart or kept stalling. There were no reports of injuries or crashes linked to the models.

The stalling can happen at bad times, such as when drivers are trying to merge onto highways.

In a letter to NHTSA, Toyota said the problems was due to physical faults in the production of the vehicles' engine control units, which it blamed on mistakes at two suppliers, one of which was identified as Delphi, the Free Press said.

"Toyota has been investigating this issue and is now considering how to address our customer concerns," the automaker said in a March 2 letter to NHTSA obtained by the Free Press. "Based upon its analysis, Toyota does not believe that the alleged defect creates an unreasonable risk to motor vehicle safety."

The automaker said the problems would always trigger a dashboard warning light, and estimated the problem would only affect 0.8% of the models in question over 10 years. It added that while some owners were "inconvenienced" by engine stalls, they were "preferable as opposed to allowing the engine to become damaged."