You should never have to replace parts blindly.
Check each part of the EGR system to identify the problem.
This covers how I do it.
The DPFE measures the pressure drop across the orfice in the EGR tube. It tells the computer what is happening in the EGR system. The DPFE connector is supplied with 5vdc and ground from the computer, and sends a variable voltage back to it. The DPFE output should be about .45 vdc with the EGR valve closed, if it is not check the wiring.
With the engine running at idle, open the EGR valve with a vacuum pump while measuring the DPFE output voltage with a meter. With the EGR full open (5 in. Vacuum)the DPFE output should rise to over 4.5vdc. This tells the computer that the EGR valve is full open. The engine should almost stall but it will recover by opening the IAC.
If the DPFE responds, hook a vacuum guage to the EGR vacuum hose and rev up the engine. The vacuum guage should display up to 5 in. of vacuum above 3k RPM. If no vacuum or very low vacuum is present recheck at EGR solenoid. Make sure solenoid has manifold vacuum at it's input line. If there is no vacuum output from the solenoid, unplug it's connector and check for voltage while reving the engine. Replace solenoid if more than 2vdc is present or check wiring if not.
If the DPFE output stays low, either there is not enough EGR flow, the DPFE or associated wiring is bad, or the DPFE cannot sense it. Check the EGR tube for holes or cracks.
Make sure the two sensing hoses from the DPFE to the EGR tube are connected properly, not damaged or leaking, and not obstructed (if the voltage goes down they are reversed). They should be the original thick high temperature silicone hoses.
Disconnect the EGR tube from the EGR valve and start the engine long enough to verify that exhaust is passing through the EGR tube. If not, use a coathanger (or a better tool if you have it) to clear obstruction from the orfice in the EGR tube. If necessary replace tube to regain exhaust flow.
Remove and verify that the EGR valve is unobstructed and opens by applying vacuum to it's nipple while blowing compressed air through it. Air should come out in large volume (no restriction). If it does not, replace.
Remove the throttle body and it's gasket and clean the EGR passages in the upper intake manifold - then stuff a rag in the intake opening and blow compressed air into the manifold's EGR port. Again air should come out in large volume (no restriction). If it does not, clean until it does.
Of course, don't forget to reassemble everything when you,re done!
