Close with your finger on the button continuously, or close with the one-touch operation?

If the EGR is leaking you'll see oily deposits in the area surrounding it.

There is a pressure sensor mounted at the side of the manifold, it measures the pressure within the manifold - important for the ECU to know. The pipe comes from the EGR valve, and it is connected to the ECU via a small multipin connector. Check the vacuum hose for leaks/blockages, and clean the pins on the connector. You could also check the actuator which is on the other vacuum pipe to connect to the EGR. Interestingly, this actuator is identical to one that controls the turbo, which is situated directly underneath the air filter box. You could swap them over to see what happens.

I would guess that with the AC on, or the car in drive, more fuel is required and delivered - and thats why the misfire disappears.


Another thing that hasn't been mentioned is the MAF sensor. You could try giving it a clean:

http://mbclub.co.uk/forums/showthread.php?t=26286