The EGR valve position (EVP) sensor can fail on this vehicle. The EVP sensor measures the EGR valve position and transmits the date to the engine control computer. If it fails, drivability and fuel economy can suffer, the Check Engine Light will commonly illuminate.Google+
Car Problem Reports
Mercury Grand Marquis EVP Sensor Failure May Cause Drivability/Fuel Economy Issues
Mercury Grand Marquis Problem
Average Mileage: 111,400 mi (75,000 mi - 150,000 mi)
Visitor, 1992 Mercury Grand Marquis
Had it in the shop several time for the same EGR valve and light on
Visitor, 2001 Mercury Grand Marquis, 150,000 mi
Had the same reading and too much vacuum on fuel sensor. We had to take the gas tank down and a lines above it was broken. $325 at the dealer for the part. Less than $40 for 2 at the junk yard. Problem solved.
Visitor, 2001 Mercury Grand Marquis, 98,000 mi
Check engine light came on took vehicle to repair shop found the erg valve was faulty.