I've been having issues with my blazer (2000 4.3 w/ 90K miles) for a few months now, and they seem to get be getting progressively worse. The engine seems to idle a little rougher than usual, but when I am accelerating (any acceleration, even pulling out of the drive), the engine begins to run extremely rough and loses power momentarily, then kicks back in, resulting in what is best described as a bucking feeling. It seems to be most evident first at 800 then at ~1600 RPMs. I originally thought it was a transmission issue, since it seemed to occur right before it shifted up to 2nd and then again into 3rd, but I get the same thing running in neutral. The thing that is throwing me off is that on the way to work early in the morning, it is bucking extremely bad, almost to the point of stalling when I accelerate from an intersection, but on the way home, after it has been sitting in the sun for 10 hours, it seems to run perfectly fine, with maybe a little less power than I remember, but no bucking or sputtering. Engine temperature doesn't seem to matter much at all...it does it the whole way. When I checked the codes, I got a P0108 (MAP sensor) and a P0300 (random cylinder misfire). I've replaced the fuel filter, the plugs only have around 20,000 miles on them, and the wires are new (replaced before I bought it). I cleaned my MAF today, and everything ran exactly the same. I did a little process of elimination work, and the engine ran the exact same regardless of if the MAF was plugged in or unplugged. It also ran about the same with the MAF plugged in and the MAP unplugged, as well as with the EGR valve unplugged. It seems like people having MAP issues were able to solve them simply by unplugging it, but that doesn't work. So, long story short, I think its the MAF that may be faulty, but I want to get a second opinion before I shell out $100. Any ideas?

 

when the egr is unplugged it runs better or worse?

 

It seems to run about the same, but it's hard to tell.

 

Wouldn't even start the other day, so I let it sit for a few days. I tried again and was able to get it started, it ran rough, so I took it in to have the fuel pressure checked. Pressure checks fine, and the shop suspects the fuel pump may be on its way out, but they're not positive so we're waiting to see (any suggestions on this one?) I drove it home from the shop this afternoon, and it ran perfect the whole way. I'll take off the EGR valve this weekend and have a look/give it a cleaning and see if that helps anything. If it isn't the fuel pump, it seems to me that some valve somewhere must be sticking to cause this intermittent problem.