Toyota knew two years ago about the engine problem behind its latest Lexus recall, even changing the spring part to correct it, but did not think a recall was warranted until recently, a company official said Tuesday.

Toyota Motor Corp started on Monday a global recall over engine defects in its Lexus luxury models sold around the world, as well as the Crown sold in Japan, moving to repair some 270,000 vehicles to replace valve springs - crucial engine components that are flawed and could cause vehicles to stall.

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In August 2008, Toyota changed that spring part, making it thicker, to prevent the problem, spokesman Hideaki Homma told The Associated Press. That is why the latest recall does not affect vehicles produced after August 2008.

Toyota, the world's top auto maker, previously thought the problem was caused by a foreign substance entering during manufacturing of the valve springs, and beefed up checks so that wouldn't happen. But the company had thought the issue was an isolated problem that didn't require a recall.

"We changed the part in August because then the problem won't happen at all, even if tiny particles enter during manufacturing," Homma said. "We are talking about microscopic particles here."

But the complaints started climbing, and Toyota decided recently they weren't isolated problems after all, but a design defect, and decided to issue the recall, Homma said.

Toyota has promised to recall problem cars more quickly to salvage a once pristine reputation now in tatters after recalls surged to over 8.5 million vehicles globally since October.

Toyota executives have repeatedly vowed to put customers first. But it has been criticized as lagging in its response to quality lapses, and was slapped with a record US$16.4 million fine in the United States for responding too slowly when the recall crisis erupted.

Auto analyst Koji Endo at Advanced Research Japan Co said auto makers routinely improve parts and technology when a product is remodeled, and the facts don't necessarily point to an intentional cover-up.

But he said that recall after recall at Toyota was devastating for its image, underlining how it had not properly paid attention to quality during its booming expansion years.

"They are paying for that now," he said. "Demand had been surging and so it was difficult to balance that with maintaining quality."