1995 S-10 4.3L vortec engine 4wd. When check engine light comes on I then start getting rough, surging idle and very hard brake pedal. Very hard to stop the truck. When the light is off, everything is okay. I checked PCV valve and hose, found melted old insulation to two wires going to MAP sensor (taped them up) still have the surging and hard braking. Can't locate EGR valve (don't know what it looks like). Sounds like a vacuum leak but haven't found it yet and probably won't be able to.

Any ideas?

 

The egr valve is on the front of the engine, just to the front and below the thermostat housing. You could have some carbon build up causing the valve to not close completely. Also check the vacuum line going to the power brake booster for leaks.

 

you might want to check out your map sensor, it sounds like it was fried causing the wiring to fry also, or vice versa. the map sensor maybe be causing a vaccum leak then causing your brake pedal to be stiff, hence NO VACCUM ASSIST in your brake booster.