Toyota Repair: 4Runner and Rough Idle, poor gas mileage, air intake system

Question
My 1990 V6 3.0L 4WD Automatic 4Runner (163,000 miles) is running rough and dying at idle.  I've taken it to the mechanic twice and it'll run better for a month or so and then mess up again.  My wires to the Oxygen sensor underneath the car look a little charred.  Could this be my problem?  I'm also thinking it might be my EGR Valve.  The car runs ok while it's cold but after it warms up, it'll die after idling for a few seconds.  I have poor gas mileage and power.  Any ideas where I should start?  Thank you, Stacie

Answer
A problem with the oxygen sensor circuit or the o2 sensor itself would make the check engine light come on so would a failure with the EGR system unless the EGR valve stays on at idle, in that case the engine will run rough and die but not turn on the check engine light, the check eng light will only come on if there is insufficient egr gas flow and not if there is too much so yes, it could be the problem.
There could be other problems related to engine misfire or a lean misfire condition, possibly a leak in the air intake system, check the intake hose from the air cleaner to the throttle body, they are known to develop cracks, especially at the throttle body end.