92 s15 rough running

just got a 92 s15 jimmy w/ 4.3 tbi 4wd 181k miles.. its running rough.. the right(pass side) injector only sprays here and their.. when it is it runs fine when not... crap... i switched the wiring from the left injector to right and it was spraying good so its not clogged.. any ideas? i was thinking maybe tps but a friend said maybe cpu is gone.. i cant afford to dump money into it guessing so any advise would be great..