Problems for specific Mercury Grand Marquis years:
Problem Reports
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1991 Mercury Grand Marquis Problems
Engine Performance Problems Due to Failed Throttle Position Sensor
The throttle position sensor (TPS) may fail. Common symptoms of a defective TPS can be rough idle, hard starting, hesitation on acceleration, poor fuel economy, and stalling.
Airbag Light Due to Failed Spring in Seat Belt Buckle
A spring in the seat belt buckle may wear or fail, causing the airbag light on the instrument panel to illuminate. Failed buckles will require replacement.
EVP Sensor Failure May Cause Drivability/Fuel Economy Issues
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.
Engine Stalling and/or Hesitation on Acceleration due to Faulty Idle Air Bypass Valve
If you experience difficulty starting the engine when cold, stalling at idle, or hesitations during acceleration, it may be the idle air bypass valve. This valve helps the vehicle idle steady when the accelerator pedal is not pressed.
Not Much Heat
I changed the thermostat and installed it correctly but usually my Grand Marquis puts out hardly any heat at all.
Intake Manifold/Valve Cover Gaskets May Leak Oil
It is not uncommon for the intake manifold and/or valve cover gaskets to develop a coolant or oil leak. Leakage from the intake manifold may result in coolant in the engine oil. Coolant mixing with the engine oil severally impacts the lubrication ability of the oil. Internal engine may result if this condition is not repaired promptly.
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