[Z U L8R]

amen @ clean the passages too
you can use a hanger, and it's only carbon, trust me there's a shit ton more on the tops of your pistons i'm sure hahaha use carb cleaner, brake cleaner will work but is not o2 sensor safe, so use carb cleaner

egr valve dilutes your cylinder head temp by recirculating exhaust gas back into your intake. you're thinking "exhaust gas is hot, how the hell does it lower my cylinder/head temps?"..temperature wise it is "hot" but in comparison to your combustion chamber it's not. just like your anti-freeze would burn the shit outta your skin...but it cools your motor, same thing. but anywho, the unburned fuel and other mixed gases in it helps cool your cylinders and reduce the chances of spark knock aka DETONATION. the hotter the cylinder temp, the more nitrous oxide (harmful gas aka NOX) is produced. therefore your egr valve and your catalytic converter work hand in hand to lower your NOX readings. for driveability and emissions purposes egr valve is a good thing. for performance purposes,where emmissions don't matter, delete egr and replace with intercooler and good tune =]

if you've ever looked at a nissan throttle body, it has coolant flowing through it. it does that to raise the intake air temp so your car doesn't run as lean. lean = power but lean also = heat, the extra fuel aka RICH cools the cylinder wall. running rich is safer than running too lean. anywho the car running lean heats up the cylinders and thus create NOX. on a performance motor , you want the air the engine ingests to be cool/dense, that's why there's intercoolers, and cold air intakes etc etc. anywho, hope you learned something :P

gl
Dave =]