rough running at times on 1991 Chevrolet S10 Blazer

Wife drives during bad weather only, so it sits 85 to 90 % of the time in the garage covered up. Sometimes when she drives it to work which is about 30 miles one way, about half way there it starts to run rough. I bring her a different vehicle to drive on into work with and then drive the blazer home. It sometimes runs okay when I drive it back home and other times it runs rough on me.[coughs and sputters, and jerks] I usually park it in the garage till the next time she needs it and it might run good for a few trips in to her job and then all of a sudden it starts acting up again. Whats wrong with it? Any help would be appreciated.

Asked by for the 1991 Chevrolet S10 Blazer
Maybe try a bottle of Chevron Techron to help clean the injectors or a tune up if that hasn't been done already
2 more answers
if that wont work. then try replacing a few parts. my cuz had the same problem. we found out that the engine was messed up. so we replace a few things.
if you have the 4.3 carb can build up in the EGR Valve and cause it to run like crap. I personally had this problem w/my 92 4.3 TBI, they can be cleaned but be careful as they are delicate inside.I also used seafoam in intake (fogged the engine) and gas tank if you do this read the instructions carefully. Also my blazer is notorious for running bad when Distributer cap is corroded Sp.?, they have no seal and draw heavy moisture. I had to replace mine almost every spring until I bought a Napa Gold.