Problem is the EGR is opening just off idle and still open when throttle is just closing which causes a rough idle for about 20 sec then the valve closes. The valve functions good, it is clean and the electric vacuumed valve is good, also new. My question is there a engine speed sensor or a hookup to a throttle position problem here that should keep the valve closed until the rpm or throttle is open further. It drive ok other then the little stumble.
Has the EGR valve been replaced? This sounds like the EGR valve has a weak return spring, a very common problem with this system. If the valve was replaced did you use Delco parts? After market EGR valves do not work correctly on these vehicles. A restricted exhaust system can also cause excessive back pressure which will push the valve open too far too soon on acceleration.
A proper EGR system control test would involve teeing a vacuum gauge into the EGR control vacuum line at the valve and checking for proper valve opening and closing at a specific vacuum specification. A good repair manual should outline the test procedure and with the proper tools this problem should be easy to diagnose. I joined alldata and found this discription of my system. I am going to buy a new GM valve Monday.
The negative backpressure EGR valve has the bleed valve spring below the diaphragm, and the valve is normally in the closed position. The negative backpressure EGR valve varies the amount of exhaust gas flow into the manifold depending on manifold vacuum and variations in exhaust backpressure.
The diaphragm on the valve has an internal air bleed hole which is held closed by a small spring when there is no exhaust backpressure.
Engine vacuum opens the EGR valve against the pressure of a large spring. When manifold vacuum combines with negative exhaust backpressure, the vacuum bleed hole opens and the EGR valve closes.
This valve will open if vacuum is applied and the engine is not operating. New valve GM not aftermarket fixed problem.Car Repair Talk's forum.
A proper EGR system control test would involve teeing a vacuum gauge into the EGR control vacuum line at the valve and checking for proper valve opening and closing at a specific vacuum specification. A good repair manual should outline the test procedure and with the proper tools this problem should be easy to diagnose. I joined alldata and found this discription of my system. I am going to buy a new GM valve Monday.
The negative backpressure EGR valve has the bleed valve spring below the diaphragm, and the valve is normally in the closed position. The negative backpressure EGR valve varies the amount of exhaust gas flow into the manifold depending on manifold vacuum and variations in exhaust backpressure.
The diaphragm on the valve has an internal air bleed hole which is held closed by a small spring when there is no exhaust backpressure.
Engine vacuum opens the EGR valve against the pressure of a large spring. When manifold vacuum combines with negative exhaust backpressure, the vacuum bleed hole opens and the EGR valve closes.
This valve will open if vacuum is applied and the engine is not operating. New valve GM not aftermarket fixed problem.Car Repair Talk's forum.
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