I am pretty sure my EGR valve is opening too soon. The EGR valve is OK because the same problem occurs with a known good one. If I just touch the accelerator it stumbles just enough to be noticable. If I plug the hose to the EGR valve the problem goes away. What could make an EGR valve open too soon? The shop manual suggests checking the intake manifold passages. I'll try that this weekend. Any other thoughts or suggestions?