'01 Olds Alero stalls while idling/making a turn?

Hello...I hope someone can help b/c I am at my wits' end with this! My car stalls out when I am idling and/or making a turn..it will cut right back on but it has happened twice while I was in traffic and most frequently when I am making a turn. Work done: tune up 2 months ago, thermostat replaced 2 weeks ago; most recently replaced my fuel filter and, in the hopes that it would fix the problem, an idle air control valve. That last part improved the problem only slightly. The MAIN issue I'm having is that when the car is hooked up to a scan tool/code reader, THERE ARE NO CODES. I've had this done countless times and get the same result. I don't want to have to continue to spend money replacing parts in the process of elimination, but that is what I'm doing. I know it could be the throttle position sensor, the mass air flow sensor, or it could be the idle air control position sensor, and a couple of other things; I'm just hoping that someone can please help me figure this out! And also if you could tell me why the scan code readers are not picking up any diagnostic trouble codes?Please help! Thank you!