Hello,
I have a lingering issue with my 87 PU. In accelerating the car was stumbling and when I would let go of the gas pedal, it seemed to backfire. This was something akin to a low energy pressure pulse through the exhaust. In reading through some of the prior threads I disconnected the EGR valve by disconnecting the vacuum tubes and plugging them. That solved the stumbling issue but it also affected the gas mileage. The engine was running too rich. Both the EGR valve and the EGR vacuum solenoid appear to be functioning. I did however remove the EGV valve and cleaned it. There was some carbon deposit but otherwise it looked OK. Anyway having placed back the EGR and reconnecting the vacuum lines, the stumbling issue has returned. I suppose I may have an intermittent issue with the EGR itself. I can certainly replace it but I want to make sure this is the real culprit first. Any ideas on what to chase? I suppose the other alternative would be to leave the EGR off and adjust the carb but two issues there. First I don't know how to adjust the carb and more importantly I don't want to violate the emission rules.