In general it's felt that having the EGR (exhaust gas recirculation) system on diesel engines is good for reducing the NOX output but bad in all other respects. It reduces economy, creates more smoke, increases problems and maintenance requirements due to clogging the intake and can reduce overall engine life. As a result of wanting greater economy I decided to stop the exhaust gas being recirculated. The problem with doing this on a modern engine is that the EGR valve operation is monitored by the MAF sensor. The only way to disable the EGR and not trip a fault code and limp home mode is to fool the MAF into thinking the EGR is still working. On another forum I saw a member Karteck was also looking into this and performing some testing on what resistance values to use to create the required drop in MAF output when the MAF should be operating. He provided the below circuit to use. The basic circuit for this comprises of two resistors to act as a potential divider and a diode to stop 12v being fed into the MAF circuit. By connecting into the EGR vacuum transducer activation wire this causes the circuit to only operate when the transducer should be operating the EGR valve. The standard circuit is a 1k ohm resistor, a 470 ohm resistor and a diode. 1/4 Watt resistors work OK. The above is for a W210 300TD but the same components should suffice for most applications, but the connections will need to be determined. First locate the EGR vacuum transducer and disconnect the wiring plug. Using a meter check which wire is the 12v feed and which is the active low signal wire. Next go to the MAF sensor and again using the meter source the signal wire, which should be Pin5. For ease of connection trace these wires back to the engine ECU. The easiest way to do this is to disconnect the connector, remove the screw in the back of the connector and prise the connector apart to reveal the wires. In practice removing the screw and operating the over centre catch will part the connector. Build the circuit and insulate the components then after locating the appropriate connections (12v, EGR active low, MAF signal) strip the insulation from the wires and solder the mod in place, then make good the insulation. You will need to disconnect the EGR transducer electrical connection, so ensure you tape it up to stop any water ingress. The final installation will look something like this, although normally the wires are tucked away by the side of the loom. The next diagram is for a ML270 just to show the connections. It's the same components, just different ECU connections. W210 300TD is: Switched 12v (sorry, can't remember which pin I used) EGR signal = Pin 35 MAF signal = Pin 21 ML270 CDi: 12v = Pin 37, plug 3 EGR signal = Pin 60, plug 3 MAF signal = Pin 24, plug 4 I think the above will work for all Vacuum transducer type EGR valves, but the connections may vary. if you try this mod please report back your connections.