I'm going to replace my EGR valve as the old ones been in there for 10 years and 140000 miles and is, probably, well clogged up and worn so I'm not going to bother cleaning and re-using it for the sake of £60. Should I disconnect the battery before removing the old one? I've read about the new one needing to be adapted. What is this? Is this something the ECU will "self learn" that something's changed, after a while, or is it more involved? 
