scott"s blazer

Start with a tune up ( air filter, distributor cap and rotor, and new spark plugs and spark plug wires ) then see how its running before going any further.

Are you getting a check engine light on it ? If so check for codes a tune up would help but sounds like it could be more then that. I would check for a vacum leaks as well a small one would cause the same syptoms. Good luck

I have a '94 4.3L Blazer that had the same problem, rough idle, hard start, bad gas mileage, EGR error code displayed, etc. Solution, in my case, was the following. At 12k mile intervals engine would begin to run very rough with a code 32 display, I think, indicating stuck EGR. I would clean it and same would happen again in 12k. Then one day my gas mileage dropped in one tank of gas about 3-4 mpg and engine ran rough. I opened the plenum and discovered both plastic fuel pressure/return line cracked and leaking which I replaced. You can tell immediately what (fuel lines/fuel regulator/CPI) is leaking by the color of the chamber inside. If DRIVER side is a light honey color - leaking fuel line(s) or hopefully less likely the CPI unit as they are very expensive. If PASSENGER side is honey color fuel regulator leaking. After I replaced both cracked fuel lines my EGR problems ceased. Note this may not apply to you if you are not getting an EGR error code because a leaking fuel line will cause a rich mixture that in turn will "dirty" up an EGR causing it to stick causing a code 32. Anyway hope this is useful info.

ITS EITHER MAP SENSOR AND OR VACAUM LINES