Hard start/rough idle

[Rowe06]

Went to look at a truck a guys trying to sell. When I first talked to him he said it had a low boost code so I figued no big deal a clamp loose letting it leak. Got there today to look at it he had it running when I pulled in and it was idling rough. He said he had changed the idm which we took the inner fender out and it did appear to be new and he had record book with paper work showing he had a new one put on. I cut it off and started it back it and it was hard ti start back. Anyone have any ideas as to what it could be before I decide anything on buying it