Gbastos

I have an 03 350z. It idles around 1000 rpm. So i took it to a mechanic to do an idle relearn and he said it would not relearn that i need a new throttle body. So i bought a new one, did the relearn that you can find online and it would work sometimes and idle at 600 rpm. But as soon as i turn the car off and back on the rpm would go back to 1000. Anyone know why? Do i need to do the relearn from a mechanic or? Thanks