I got a 89 gmc sierra i ran the vin# on it and i guess it originally came with a 305 in it now the guy that owned it before me put a 350 in it and always had a problem with it ideling and he blew that motor up so i put another 350 in it and still same problem shitty idle. Would that have anything to do with the computer do to the fact it was originally programed for the 305 and what do you suggest me doing to get it to run better besides checking for vacum leaks.