What EXACTLY was/were the service fault(s) returned? Service fault codes for the EGR system can be caused by vacuum leaks, a faulty EVP sensor or EVR solenoid, or the EGR valve itself sticking (open or closed) or not opening or closing fully (due to the same reason it would be sticking - carbon buildup). If you're automatically looking at the EGR valve without testing the entire circuit (a VOM and vacuum pump are two tools required - do you have them in your toolbox??) you could be wasting some serious coin.
Sometimes EGR valves will work properly once they are cleaned-out. Sometimes they will not. It's a crap-shoot. Be prepared to fork over the coin for a new one, IF that's really what the problem is.
1979-1993 Fox Capri and Mustang VIN Decoder: foxchassis.com
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