Okay I'll start with the stats, 2004 blazer 4x4 98000 miles. I have replaced the cap, rotor,wires, plugs(AC DELCO), fuel filter, pcv valve, map sensor, alternator, flushed raidiator, replaced thermastate(sp) and cleaned the mass air sensor and it still runs bad, I have always done oil changes and air filter changes. The check engine light stays on all the time, flashes when I hit the gas. I scanned it and it said there was a cyl 2 misfire, that was all. I was getting 19 to 20 mpg, now down to 12 to 15 mpg. Now at idle the truck runs the worst, whole thing shakes very bad and rpm dips down to 300rpm but does not die and it has NO trouble starting. When I am speeding up there is a loss of power and less vibration. I just dont have the time to take her to a professional so any advice will be appriciated.

 

im thinking coils. i could be wrong.

 

Check to see if plug wires are seated properly, also to correct firing order.

 

I would recommend some quick and cheap preventative maintenance. Buy yourself a can of sensor safe carbon cleaner, a new EGR gasket, a can of MAF specific cleaner, and make sure that you have a good set of metric sockets with extensions handy. Remove the Throttle body, the EGR valve, and the MAF sensor and clean them all very thoroughly.

The MAF sensor is very sensitive and if coated with dirt and other junk, it can throw off the entire operation of the vehicle.

The EGR valve can get gunked up with carbon deposits from the exhaust flowing through it. These deposits can hold open the EGR pintle valve causing various drivability concerns. Clean it as best you can with the sensor safe carbon cleaner.

With the throttlebody, make sure that you remove the IAC valve and clean it and the bore it goes into with a toothbrush and some of that sensor safe carbon cleaner.

Also, if you do not know when the last time it had a tune up, it wouldn't hurt to throw on a set of plugs, wires, and a new cap & rotor. You should atleast pull a few plugs and check their condition, but I typically will just replace them when I pull them because my time to pull them is worth more than the plugs are. If anything, I have a set of used plugs incase I do something stupid like snap a plug off working on something unrelated. LOL

Good luck and let us know if you have more questions.