I just got a 1997 SC300, and the check engine light just turned on which made me very disappointed!

Aside from that, whenever I am at a red light and have the air conditioner turned on, my engine will make this wired jumping noise/movement. Its a very small jerking movement last about a second, but does it every time I am idle with my car on drive and the air conditioner is on. Does anyone know what may be causing this or how I can go about fixing it?

Thanks!