Just about the only cause is an inoperative EGR valve or control system. That is the science behind the EGR valve was to lower NOx. I'm no expert an this era of vehicle, and don't know what controls it, whether it be a ported or thermostatic vacuum switch or what. Check that your vacuum connections are made, and proper. Check and see if a vacuum signal is reaching the EGR valve and when. Pull up on the EGR valve diaphragm from below the top and see if the engine roughens or stalls. I don't know if you can apply vacuum to the valve to see if it opens/holds vacuum. It may require exhaust backpressure to assist in it's opening. There are two types of valves, a negative backpressure, and a positive backpressure. It would be stamped NEG or POS on the top by the part number. I don't know without some research, the operating principles of either right now.
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Thursday, December 17th, 2009 AT 10:07 PM
