I've been battling an EGR error on my wife's car (2000 Lumina). The man I bought it from had replaced the EGR to no effect. I've had the EGR off a couple of times myself and cleaned out everything the best I could using some wire and aerosol seafoam deep creep which my mechanic friend recommended. Tonight I ran a pint of regular liquid seafoam through the vacuum line off the pcv valve and in the process found a crack in the pcv elbow. Could this crack could be the cause of my problem?? Off to the junkyard or dealer tomorrow...

I see lots of postings saying to clean the carbon buildup but most are pretty vague as to what needs to be cleaned.

Any unmetered air entering the engine can skew the egr feed back inputs to pcm.