Here are the codes that I got
PO401 - egr system
PO502 - vehicle speed sensor
PO506 - idle speed higher/lower than expected
PO507 - rpm higher than expected
PO601 - improper reprogram on ECM/ECM failure
PO602 - ECM not programmed

I do not have alot of money for what seems to be a costly repair. What I am thinking is that one of the above problems maybe causing the other codes to appear. So any insight as to where I should start? I was thinking that replacing the vehicle speed sensor would clear up codes 506 and 507. I am not to sure about the 601 and 602, should I have the ECM replaced? or just reprogrammed?

Thanks for any information