1995 Chevy Blazer what might the problem be and how much wi

lately when im stopped or going slow the rpms go all the way down and the car just turns off even when im still in drive if i press the gas petal a couple times when its going down, it wont shut off. my check engine light comes on also. but if im on the highway it wont shut off and ive noticed a ratteling sound under the car behind the oil filter maybe?? can you please get back to me on this because will try to rip you off. I'ts good to know u guys will take questions like this makes me feel like not all business has there hand in your pocket and just like to provide services for the good of people