99 Camry Stalls

Hi Ppl, I have a 99 camry LE which has 90,000 miles on it. It runs great except once in a while it stalls. it stalled once when i was in a stop light and another time when i was making a right turn. but the car starts back immediately and drives very smoothly. I am not sure what the problem is. I took it to a auto shop and did a computer diagnostic but then that didnt show up any problem and the car mechanic gave me an invoice for $250 telling me i have to change my plugs, clean my throttle plate and fuel injectors. Basically even the guys in the auto shop didnt know what the problem was exactly! I am not sure what to do! I already checked the air filter and thats clean!! this doesnt happen very frequently...just abt 2-3 times in 1000 miles!! can somebody help me? Thanks, Venky