Engine runs hard
 

I have a 03 4wd blazer with 193k on it. The engine is running very rough and I have to hold the throttle to get it to keep running. I am not able to drive it as I can not get my rpms above 2k. Even with the throttle floored my rpms fluctuate and the engine still start shaking and will sometimes die. I have replaced the fuel filter. Spark plugs, spark plug wires, distributor cap and just replaced the fuel rail and still have all the same symptoms. Only code that I get is a random engine misfire code. Im pretty much at a loss here and am hoping one of you guys can help me.

Start with the basics. Do a compression test on all cylinders. Also, look for obvious vacuum leaks.

My milage was about the same as yours. It did not run to well, but would go down the road. I had purchased ac delco wires from Amazon and I also had random misfires. Try looking at your engine at night and see if you see sparks jumping. I had two that were jumping at times. Amazon sells two sets of AC delco wires and one is far better than the other. Timing chain stretch on these engines on high miles and throw timing off a little. Made a major difference after changing. But I doubt that this is causing the problem of rough running, it will just be a lack of power.
Compression test is a sure way of saying you six cylinders are ok! I hate taking spark plugs out of these engines. I don't know if you used ac delco cap or not? I would look under the cap for cross firing lines. It will certainly cause the bad running engine. Also I don't know if this problem started all at once or just overtime. Will it idle at all? If it does you can pull a wire at a time and see which cylinders are misfiring. Two together could be a bad head gasket.
Vacuum leak will cause it not to idle. You can spray wd 40 checking for them. Do around your intake were it mates to the head. See if you can get a change. Also with that milage have you changed the intake gaskets, if not it is time. Do you lose coolant and have to add?
If no idle and will not go over 2000 rpm, have you checked the firing order? Also your EGR valve is pretty easy to take off and see if it is working. New gasket is cheap, check you tube.
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