LOS ANGELES -- Alan Seider has owned 11 Toyotas since 1982, but his 2006 Avalon likely will be his last.

He says quality glitches have bedeviled his Toyota sedan, which he has driven less than 6,000 miles since he bought it last July. His dealer could not solve the car's problems. Toyota headquarters stonewalled his appeals, he says.

"There have been significant throttle control and transmission hesitation issues," says Seider, 45, a computer consultant from Roswell, Ga. "I've isolated 15 different rattles in the body work."

Seider is far from alone. Internet chat rooms such as Edmunds.com Town Hall are littered with complaints from Toyota loyalists about the redesigned Avalon, which went on sale in February 2005.

The Avalon's launch problems point to a larger issue. To meet demand, Toyota has added factories in North America and thousands of new employees. Executives are worried that Toyota's rapid growth may dilute its quality standards.

Toyota and Lexus divisions still exceed industry averages in various studies that measure quality. Toyota predicts that the Avalon will score well in J.D. Power and Associates' Initial Quality Study, to be released in June.

But the quality gap is closing. And Toyota recalls have spiked in the last two years.

Every production line produces its share of lemons. But Toyota already has issued a string of technical service bulletins to dealers to fix Avalons on the road. Changes are being made on the assembly line. Toyota representatives acknowledge there are some teething problems, but decline to call the Avalon a problem car.

The Avalon is the Toyota brand's most-expensive car, starting at $27,355 including destination charges. The redesigned 2005 model was embraced by consumers; Toyota sold 95,318 Avalons last year in the United States, up from 36,460 in 2004. Avalon sales peaked in 2000 at 104,078 units. It is assembled at Toyota's Georgetown, Ky., plant, alongside the Camry and Camry Solara.

It's a car-buying axiom that one should never buy a car in its first year of production, before the bugs are worked out. But in recent years Toyota and Honda largely disproved that old saw, delivering nearly bulletproof vehicles from Job 1.

Now the Avalon redesign is showing that even mighty Toyota can slip up.

Kevin Clingenpeel, a 37-year-old insurance litigator from Fort Mill, S.C., loved his Avalon for the first 2,000 miles. Then the transmission shifts became erratic, especially in cold weather. The engine developed a persistent knock, which could not be cured by changing grades of gasoline or by using a fuel-injector cleaner.

"I pulled up next to a Ford F-350, and I could hear my valve train clicking louder than his diesel," said Clingenpeel, whose Avalon is his family's third Toyota.

Clingenpeel says his dealer gave the car "a wink and a nod" when he brought it in three times for repairs. Clingenpeel then appealed to Toyota headquarters to send out a district service manager. Toyota refused. Now Clingenpeel is looking to sell the car.

"It's sad because there's a nice car hiding behind all this," Clingenpeel said. "But this is not up to snuff from what I would consider from Toyota."

The Avalon's problems have drawn notice from Consumer Reports magazine, which has for years given the Avalon high marks.

While still giving the 2005 Avalon its highest scores in most categories, the magazine's overall quality rating for the car was average because the Avalon scored below the Buick LaCrosse, Kia Amanti, Ford Five Hundred and Mercury Montego.

Anita Lam, data program manager for Consumer Reports' auto test center, said problems with the Avalon cropped up in steering, suspension and body integrity.

"These are first-year teething problems. We anticipate the second model year will be much better," Lam said.

Toyota spokesman John Hanson called the Consumer Reports ratings "the sum of small irritations more than anything else."

But Hanson acknowledged that Toyota has been concerned with the initial wave of quality problems for the car. Toyota's priority has been to find and remedy problems, get the fixes to the production line, and issue technical service bulletins so dealers can fix the faults on vehicles already on the road.

"The Avalon is the most complex vehicle Toyota Division sells, so just by definition it's a problematic vehicle," Hanson said.

The Avalon's transmission lurch is especially noticeable in low-speed crawls during rush hour, Hanson said. Previous Avalons had problems shifting smoothly at high speed with high engine revs. Toyota fixed the high-speed lurch by changing software algorithms, but the adjustment caused a low-speed lurch.

The low-speed problem "is all software," Hanson says.

Some customers are voting with their feet. In Seider's case, he replaced his wife's Toyota Sienna minivan with a Honda Pilot. He doubts he will replace the Avalon with another Toyota.

Said Seider: "I am so disappointed in Toyota. I've had previous first-year vehicles, but nothing like this ever happened. Toyota's build quality has declined in recent years, and there seems to be nothing the dealer can do. Toyota has reached a size that they've lost sight of the individual customer."

The Avalon's launch problems point to a larger issue. To meet demand, Toyota has added factories in North America and thousands of new employees.

"The Avalon is the most complex vehicle Toyota Division sells, so just by definition it's a problematic vehicle," Hanson said.