Tune Up

I have a 89 cherokee and this will be the second summer of owning it. Last summer the thing just dead up stop running. I changed all of the sensors possible that could be changed and it still wouldn't run. I took it to a mechanic and he said it needed a tune up. I didn't believe him at first. After the mechanic closed gave the thing a tune up in the parking lot and sure enough it started up. Early this summer I noticed that the enigine wasn't running right and it felt like it was back firing as you drove down the road. Finally, it really started run like crap and after talking to people I gave it a tune up. I changed everything but the wires because they were high end wires with a little over a years use. After the tune up it still ran like crap. So, I began to think the injectors were bad. After finding out it cost a arm and a leg for injectors, I found out I have a life time warranty on the plug wires. I put the new wires on and the thing and it fired right off and drives like I first got it last summer. I am assuming now that this thing needs a full tune up every year in order for it to run right.