Carbon buildup again in EGR passages - '93

I've noticed that carbon is building up again in both passages leading to the EGR valve, and in the valve itself. I just cleaned everything out pretty good a few thousand miles ago. The engine is running good, temperature doesn't go above 50%, and the gas mileage is between 42-47mpg so I don't see any adverse affect from it. With very high mileage, I'm reluctant to fix sometime unless I know it will fix it for sure. Guess I could:
1. Leave it along and clean it out every so often.
2. Replace the EGR value and may the other doohickey downstream from it.
3. Change the O2 sensor - if engine is running rich. Actually did buy a new O2 sensor but have not been able to get the old one off.
4. What else could be causing this rather quick buildup?

Jim

I, personally, would point at the oxygen sensor. If there's that much carbon buildup in the EGR, imagine what your O2 sensor looks like. Get a breaker bar, and a 2 foot exhaust pipe to slide over the breaker bar for more leverage. Heat the sh@# out of the exhaust manifold with an acetelyne torch(oxy-acetelyne if available), then don't lean into it and brute force it, but rock it like an impact wrench. You'll shatter the socket just forcing it. If you can, have someone heat the manifold while you twist the sensor. A standard o2 sensor wrench will break trying to apply that much torque. What I usually do is break the stem of the sensor off, and use an impact socket(very thick walled black steel) on the sensor. 1/2" drive.

Good info - thanks. I think I will take another shot at getting the O2 sensor out, at the next oil change when the oil filter is out of the way. Jim