How do you clean an egr valve and where is it located?

Generally, an EGR valve is found high-rear on the motor. They can quit working due to carbon build-up on the internal shaft which causes them to stick in the open position and are hard to clean. Try spraying DEEP CREEP into it to loosen it up, then move the diaphragm by hand. DEEP CREEP is sold by the SEA FOAM companay and is found at marine dealers.