Which parts fail
Components named in complaints (accelerator pedal, throttle, sudden acceleration, cruise control).
Mileage when the problem started
Owner reports
Selected complaints filed with NHTSA by 2005 Mercury Grand Marquis owners, lightly cleaned up (personal details are redacted by NHTSA).
On [redacted] I was driving this recently purchased Grand marquis . On [redacted] here in San Antonio around ten at night I hit the brakes and something under the hood compartment blew up and it cocked the car . I was trapped inside and when I finally was able to get my seatbelt released I had to break the window with my head . The previous week I reached out to ford and they told me they would address the issue and that they would call me back and that was to no avail. i reached out to ford and at first I was told I would be helped and then a man came on the phone yelling that my vehicle . I need help with resol this issue . My car is totaled and I'm hurting and it's because of a car with recalls that are a fire haz and dangerous to be put on the road Thank you and God Bless . …
This is a serious safety hazard that could result in death or injury. If I hadn't escaped in time, I would have been killed. I am urging the NHTSA to investigate this defect and take immediate action to remove these vehicles from the road. Others may not be as lucky. This issue is life-threatening, especially because the fire started while the vehicle was in motion. These vehicles must be recalled and removed from use before more people are injured or killed.
I was driving I pressed the cruise control to set it but the vehicle kept accelerating and as I was pressing on the brake it wouldn't disengage it kept accelerating I kept pressing the brake frantically and THANK GOD it disengaged.. I never touched the cruise control again
While parked at the end of her driveway, waiting for oncoming vehicles to bypass, the vehicle automatically accelerated, and made a half turn at 40 miles per hour. The vehicle, as a result, hit a tree. As a result, the windows were damaged, the front seats, where the occupants were seated, while wearing the seat belts, were thrown to the rear portion of the vehicle. She has had the vehicle inspected by her insurance agency ( safeco) [engineer] ) who stated that this is definitely a result in an ECM manufacturers' defect. As a result, the vehicle is completely damaged. The occupants sustained severe whiplash, and pinched nerves. She can no longer place weight on her feet, which could result in severe back pain. She has had both knees replaced. She and her husband, have not been able to contact the manufacturer as of yet. The failure and current mileage 13,000. …
Arrived at son's home and stopped in driveway with foot on brake when vehicle suddenly accelerated uncontrollably, spinning wheels in gravel driveway. Driver swerved to avoid hitting garage and ran head on into a pine tree resulting in severe damage to entire front end of vehicle (expect vehicle to be considered a total loss) and injuries to the driver and two passengers. Both driver and passenger airbags deployed. Prior to arriving at destination, driver had used the cruise control on the vehicle. Vehicle has not yet been moved and am currently waiting for insurance adjuster to inspect vehicle. Both driver and front seat passenger suffered severe bruising on face, arms, chest and abdomen, presumably from deployment of the air bags as well as from the seat belts. Rear seat passenger suffered a contusion on the forehead and a sprained hand. …
The vehicle was purchased on January 26 2006 new with lees than 100 miles on it. While at a complete stop in a parking place with my right foot on the brake pedal and hand on gear shift to place the car in park in front of a nursing home. Suddenly the car accelerated forward out of control with enough speed in the short distance to go through a wall into a room of the nursing home. Luckily the room in the nursing home was unoccupied. I did suffer an injury to the top and right side of my right foot, when I attempted to pull the accelerator up with my right foot and placing my left foot on the brake pedal. The car did not stop accelerating until the impact into the nursing home. The car was towed to the dealership the same day and the owner of the dealership and service personnel was notified of the possible defect. To this date the dealership has not responded to my concerns.
Unintended accel. Sometimes when I step on the brake the car accelerates instead. At first I thought it was me and my big feet. After some internet research I find it May be common as the 2005 gets older. I asked if brke pedal could be adjusted so that there was no interference with the gas pedal, I was told no. I had the master cylinder replaced, minimum improvement. One day I "shot" across us19 in ross township when I braked. Instead of stopping at a red light, I kept going until I cleared traffic in both directions ruining 2 wheels & tires - subsequently repaired. The car now sits in our driveway, after some other occurrences without incident. I'm leary of driving it & don't want to sell it & get someone injured or killed. Fortunately I have a 2004 sable which I drive daily with no such problems! Ideas?
Tl* the contact owns a 2005 Mercury Grand Marquis. While driving approximately 5 MPH and then depressing the brake pedal to slow the vehicle down, the vehicle accelerated without warning. To avoid crashing into the preceding vehicle, the contact was able to veer to the right and continue driving. There was no warning indicator illuminated. The failure recurred three times. The vehicle was taken to porter Ford (600 ogletown rd, newark, de 19711) where it was diagnosed that the throttle body motor assembly was sticking and needed to be replaced. The vehicle was repaired. The manufacturer was not contacted. The approximate failure mileage was 39,000.
Tl* the contact owns a 2005 Mercury Grand Marquis. The contact stated that while stopped at a traffic light, the vehicle accelerated independently. The contact stated that it became difficult to keep the vehicle from moving forward. The contact stated that the brake pedal was depressed but failed to stop the vehicle. The contact was able to slow the vehicle by placing the shift lever to the neutral position. The vehicle was not taken to be diagnosed or repaired. The contact stated that the failure was intermittent. The manufacturer was notified of the failure. The approximate failure mileage was 146,784. Updated 01/05/17
This has been a dangerously recurring engine accelerating problem while at rest or moving/coming to a stop on streets or highways but always while attempting to brake or hold in place. The brakes won't stop it, only turning off the ignition and restarting works. Barely avoided several accidents, so far. My Ford dealer has inspected the systems and my foot placements with out finding a problem or a solution. There are over 30 complaints regarding this problem in your database, some with serious injuries. After all these years, how can this issue be escalated before there is a fatality? Please respond asap.
Acceleration complaints in other Grand Marquis years
Frequently asked questions
How common are acceleration problems on the 2005 Mercury Grand Marquis?
NHTSA has 39 complaints about the speed control & acceleration of the 2005 Mercury Grand Marquis, 8% of the model year's 488 complaints. The component named most often is accelerator pedal (3 mentions).
Is there a recall for 2005 Mercury Grand Marquis acceleration problems?
No. NHTSA lists no speed control & acceleration recall for the 2005 Mercury Grand Marquis, though it has 4 recalls for other components. If the problem is widespread, a repair may still be covered by an extended warranty or a manufacturer service bulletin — ask a dealer.
At what mileage do 2005 Mercury Grand Marquis acceleration problems start?
Half of the complaints with a recorded mileage happened before about 18,000 miles, and 57% before 25,000 miles.
Is it dangerous?
Owners linked 13 crashes, 3 fires and 12 injuries to speed control & acceleration problems on this model year. If you notice symptoms, have the car checked before driving further.
Source: U.S. National Highway Traffic Safety Administration (NHTSA) — owner complaints through October 20, 2026, recalls and defect investigations; fuel economy from the EPA. Complaints are unverified reports and are not proof of a defect. How we rate model years.