'97 E300 codes

[StevenB]

What a great site! It reminds me of the Ford-diesel website. Lots of good advice on both sites.
I am the second owner of this car. We got maintenance records with it. No problems until a month or so ago.
(Car has 85K miles) It began lighting the check engine light and setting codes. We cleared the codes and it reset code P1475. Some vacuum lines were replaced. It then set codes P0200 and P1475. The switch-over valve (002-540-06-97) was replaced. Now it has set code P1476, and the independent shop doing the work is telling me that the intake manifold is probably carboned up due to the combined function of the crankcase ventilation system and the EGR system both dumping into the intake manifold. Oil fumes mixing with hot exhaust gases and making carbon. Oddly enough, the original owner did have to have the manifold cleaned out once before. It seems that the carbon interferes with the operation of a set of air management valves in the tuned intake manifold. Thank you, EPA. I guess that I have a continuing problem if this is the case. If this is the problem and we get it straightened out, I am thinking of disableing either the crankcase vent system or the EGR setup to prevent the formation of carbon in the future. Is this problem common? Is there anither solution?
Do the codes I have described to you indicate this problem?
The car runs fine with or without the check engine light.
Power and mileage are great.
Thanks in advance if you can help me with this.
SBB.