Sorry for the delay!
I do this on my spare time. My boss does not appreciate it if I do this at work so I came home on lunch to answer any question waiting for me. I just got home now. Sorry, again.
If the engine stumbles when vacuum is applied to the egr valve it sounds like the air passages are not plugged.
Here is the test that ford gives to the technicians for this particular problem.
EGR Control/Vent Solenoids
1. Start engine and allow to reach operating temperature.
2. Turn ignition Off.
3. Connect a suitable hand held vacuum pump to the EGR valve vacuum supply port
4. Start the engine.
5. Gradually apply vacuum to the EGR valve vacuum supply port. The engine should run rough or stall as vacuum is applied to the EGR valve.
Pressure Feedback Electronic & Differential Pressure Feedback Electronic Systems
1. Ensure all vacuum hoses are properly routed and securely connected, and replace any that are cracked, crimped or broken.
2. Run engine until normal operating temperature is reached.
3. With engine running at idle, disconnect EGR vacuum supply and inspect for vacuum signal. EVR solenoid has a constant internal leak. A small vacuum signal, less than one inch at idle, should be noticed.
4. Install tachometer tool No. 059-00010, or equivalent.
5. Disconnect IAC solenoid electrical connector.
6. Disconnect an plug vacuum supply hose at EGR valve nipple.
7. Start engine and run at idle with transmission in Neutral, then observe idle speed. If required, adjust idle speed to specifications. If engine will not idle with IAC solenoid disconnected, provide an air bypass to the engine by slightly opening the throttle plate or by creating an intake vacuum leak. Do not exceed a typical idle RPM.
8. Slowly apply 5-10 inches vacuum to EGR valve nipple using hand held vacuum pump tool No. 021-00014, or equivalent.
9. With vacuum applied, ensure idle speed drops more than 100 RPM and returns to normal, within 25 RPM, after vacuum is removed.
10. Unplug and connect vacuum supply hose at EGR valve.
I think you really need to get a digital voltmeter. You are going to want to see about 1.0 volt, or .5 volt (depending on which one you have)on the signal wire at idle with no egr flow.
If you do not, the sensor is bad and needs to be replaced. I have seen these things come bad out of the box.
ITs just a circuit code. Its not saying that the ports are plugged up (or low flow).
This is the definition for this code is:
Code 327-Delta pressure feedback EGR, DPFE, is below 0.20 volts