have a mazda 6, automatic, 2005, 150,000 miles and suddenly car was hard to start and stumbled and stalls, towed to pep boys, they said it was a bad throttle body, replaced, drove for 4 days, car stalled on highway, same problem, towed back and replaced trottle body this story happened 2 more times, each with a new trottle body, now they say the problem is the computer and it is a dealer only item. any ideas?