GMC Jimmy problem

look for a vacume leak. buy a can of carb cleaner and start sprating vacume lines and then the intake where it bolts to the head on both sides. if you hear a stumble theres your leak. also when you do a tune up you should always do a compression check. how did the plugs look? were they all burning equal, hot, or fouled

yeah we did that there were no leaks in the vacuum lines when we did the tune up. the spark plugs werent even all the way in i think my boyfriend said it was only running off of 2 or 3. he used to be a mechanic so he could tell you way more than i could. we replaced some sensors, the computer, and the distributor and none of that seemed to help it a ton. it did help a little and after we replaced those it quit throwin 4 codes and is not only throwin 1 which is code 42. when we replaced the distributor we found a part that was put in upside down from the previous owners lack of knowledge of mechanics. we started to recheck things today and there seemed to be a leak coming from the egr valve so we took it off and it was actually plugged so bad that i didnt even know the square hole was square until i touched it and crap just crumbled off then my boyfriend started scraping and cleaning it out. so now he has that all cleaned out, he said it seems to be running a lot better, we dont have to wood it to the moon to get the damn thing started and it is actually staying running so far. but when i get more information i will post again and let you know what Gods Mechanical Curse is doing. thank you for your help!!! :)