Rough idle on a subaru justy

I looked in search first before posting and couldnt find what i was looking for. And was wondering if hooking up your vacuum switch would change your idle speed on a subaru justy efi? See I had a mechanic find and install a new japanese crate motor and the oil pan just wouldnt stop leaking he got the car while under warranty and had it for long periods of time and still didnt fix it. The warranty is no longer and i just got done paying him to do it again and when i got the car back it now has an exhaust leak and stalls out. Has anyone ever had this problem. I am just regretting going to a mechanic and paying out the ears. I tried to find a motor for almost a year and couldnt. Any advice would be great. Or stories.