yaris 2008 loses power on slow speed with ac

[usmanimtiaz]

I've toyota vitz 2008 automatic, Recently my car loses power on slow speed with ac on and it vibrates a lot before shutting engine off . I've replaced injectors, plugs and installed a new battery but the problem is still there. yesterday my mechanic said this could be because of bad transmission fluid so I asked him to change the transmission oil but it was insane the problem just won;t go he finally gave up on my car by saying the only thing left is throttle body which im not sure about because there's not fault code in the ecu about it and if we replace it im not sure if it will solve the problem. (since int's an expensive part and I can not return it )
Im looking for suggestions if anyone has ever experienced this problem before, is it a bad throttle body? should i go ahead and replace it?