89 fullsize blazer

Hi

Im new to the tbi system and am having some trouble with mine, it surges back and forth as i drive and at idle. the idle seems low and Im not sure how to adjust it or even if i can on this system. How do I read the codes or even check them? I heard of a paper clip way but want to be more sure before i start messing around with sensors and such. Ive already replaced the fuel filter thinking that was the problem but no such luck. regualtor maybe? Is the regulator inside the tbi? or on the fuel line?

Any help would be awesome