There are a couple bad designs with the CRD. One of them is the oily crankcase fumes are dumped back into the air intake. This globs up the intake and sensors. A popular mod is to vent the crankcase to atmosphere.
I used a length of 3/4" copper tubing connected to a hose, which is in turn connected to the crankcase vent. The tubing goes into the frame. A simple and effective mod.
If you look in the lower righthand corner you can see another good mod...disconnecting the MAF sensor (red arrow). The only purpose this sensor serves is airflow feedback for the EGR system. Unplug the MAF sensor and the computer shuts off the EGR since it can't monitor it. The result? Better driveability, mileage, and no exhaust soot being dumped back into the intake. The check engine lights comes on, but there is no limp mode or degradation.