If you're still having this issue you can send me a message, i run a 3800 specialist shop called S&S Performance in central NJ you can always arrange to drop it off or stop by to have me take a look at it, i don't charge for trouble shooting either

Also, if your MAS Screen is damaged, bent, notched slightly or its been removed all together it will throw this system too lean code and cause a rough idle as well just to help point out the less obvious things to check