So I ran a KOEO, and KOER test on the 2.9 today. Dont remember which test yielded the 31, pretty sure it was the KOER test. Anyway, I had a code 33, so I replaced the gummed up and very nasty EGR valve, 3 days ago, with a new one. Today I have a code 31. Any ideas, and what is the proper way...