Mitsubishi Repair: Check Engine Light, fuel filter replacement, valve plugs

Question
My "check Engine" light has recently come on. This has happened before and I have been told that my EGR valve is not operating correctly, or that I may need a full blown tune-up with new plugs and plug wires.(The local Auto Zone tech plugged the car into his hand held diagnostic device and it read "EGR valve flow is malfunctioning") Several months ago, another shop took the valve off, "cleaned it up", put it back on the car, and the light went off, but the car continued to run roughly. Any ideas? Also, where can I purchase a service manual? Also, if I were to do a full blown tune-up, what would that consist of? I've learned to be leary of shops,and if there's any way I can replace anything on this car, such as the EGR Valve, plugs and plug wires, I'd like to try. (The plugs and wires I know have not been touched in 18 months--and they look easily accessible. What can you suggest?

Answer
Denis,
Service manuals for many cars are available at places like AutoZone; Haynes and Chiltons are the common publishers.  Since you didn't specify a year, make, model, or style of car that you have, I can't really tell you if they even make an aftermarket service manual for your car.  But if you want an official manual, you can always purchase one from a dealership.

Cleaning an EGR valve can sometimes help, but if the valve is simply not working, you'll want to replace it.  A tune-up may help.  Usually that consists of replacing the spark plugs, plugs wires, distributor cap (if your car has one), air filter replacement, fuel filter replacement, and various fluid top-offs.  All garages have a different list of items set for their "full tune-up".  You'll just have to ask exactly what they'll be doing.  But plugs and wires are pretty easy to replace.  But get a service manual before you attempt any work on your car.  It may offer some tips and tricks for your specific car.
Good luck!