The Mercedes Service Manual for the M112 engine would be the best place, if it is anything like the manual that I have on the M115. Very detailed with pictures. The procedure is really easy, though. The EGR valve is located on the rear of the passengers side of the engine. The valve is held by two torx-head bolts and the flexible tube is attached to the intake manifold via a flange and two torx-head bolts. You have to remove the engine cover, the flexible intake ducting between the mass airflow sensor and manifold, and the wire to the EGR valve to gain access. I also found it easier to get to by removing the wire to the nearest fuel injector to gain access to the bolts and make removing the wire to the EGR easier. After that, you have to loosen the tube connection to the EGR valve, pull the wire to the valve, and the vacuum tube going to it. After that, remove the two bolts to take the valve off. Remove the two bolts in the tube flange and snake the tube out of the intake with a twisting motion (it is a complex shaped snorkel going down into the manifold probably about 8 inches). If it is clogged, you will see the carbon plugging the end after it is extracted. While you have everything off, take a screwdriver and delicated pry up on the diaphragm in the EGR valve and make sure it is free to move. That was what was wrong with my EGR valve itself. I put a new one on because it was in my hand and I got it cheap, but I could have cleaned the old one after freeing it up and probably been OK.