Hey everyone, I just want to say thanks for responding if you know what could be going wrong.

Skip to the second paragraph if you dont want to read the backstory.

This is my senerio, I got a 1999 4.3 Blazer 4x4 4dr form a coworker about a year ago. This truck was not being used by me but my father who was doing all the repairs that it needed. The previous owner never took care of the truck. It was slammed with the torsion bar bolts removed and blocks in the back. The Transfer Case and CV shafts where replace and so was the oil pan because it was soo low that it scraped the ground. Fixed the suspension to stock also. I just recently got the truck back from my father said that since he tryed to fix it, it had a low idle and felt really slugish. I took a look at the spark plugs and replaced them all. The passanger side sparks where good but the dirver side 1 and 3 cylinders where the wrong plugs, smaller gap. The 5 cylinder plug was the correct one but it had lots of black residue from non burned gas as did 1 and 3. It does not feel slugish as it use to. The thing is that it still idles low and the only codes i get now is P1133 and P0131 and P1351. P0131 is low voltage at the first o2 sensor. P1351 is that ther is an open on the circut but I belive that is because I was disconection some sensors. P1133 is that o2 sensor is bad or somehting related to the wireing of that sensor. My guess from taking it out previously is that it is bad. But I dont want to take a chance and buy a new one resulting it to not be the problem.

I read that there is a tan and white wire that is behind the firewall passanger side of the truck that if you unplug it takes the truck back to base timing taking the sensors out of the loop. But that is in the older gen blazers and mine does not have this wire. I was wondering if there is a possible way to check do the same in these style of newer blazers??? Reason being is that if there is a bad sensor the trucks timing is being adjusted with the sensors in the loop, but if you take the sensors out of the loop and take it to base timing I can see if it is trully a bad sensor or a mechanincal problem in the trucks engine. If you guys know of a way to do this please post a responce. Really tired of messing with the truck already.

 

So with the 99 the timing is fixed but I found myself having nearly all the same issues you are, bad milage, super sluggish and would really suffer on hot days with pretty much evey error code you have. Found out that it's very common for the connection that attaches to the sensors to go bad giving a lot of false codes and causing it to run rough as the rattle along. I did have to change my mass air flow sensor and the cam sensor at the bottom of the engine, the rest were the plug connectors that needed replacement. I also like you changed all my plugs (including the wires, distributor and cap which probably wasn't needed) . I was still having a sluggish start especially on hot days so I replaced the fuel pump which did make a huge difference but do that last when theirs not much fuel in the tank. Also I found a hole in the return fuel line right under the frame just ahead of where the fuel filter sits ( theirs a lip in the fame the hose had been rubbing on where they make the bend following the frame) after I fixed that it ran like a new machine, what crazy is I never would have known if I didn't notice a lite moisture when changing the filter right after driving it evaporated so fast and never dripped, changed my milage from 8-15mpg to 18-23mpg. I also changed the air idle control valve (its pretty easy and cheap for peace of mind) the ignition coil too. But if you replace the ICM (ignition control module) don't get a cheap amazon one get a true OEM part it's not worth the headache and can cause the vehicle to not start when hot, to run improperly at idle and to randomly die while driving(yup I leaned that the hard way). For a little free low end horsepower you can also do the throttle body mod theirs quite a few videos on youtube how to do it.