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 2008 Mercury Mariner owners, lightly cleaned up (personal details are redacted by NHTSA).
Same results of the consumer satisfaction program 13n03. A defective throttle body. Car began to stall/choke out while accelerating. It continued to do so until it finally left me on the side of the road. Ford is aware of the problem but because my car was built at a different time/plant does not offer assistance for a known unsafe problem. This started on the freeway and continued after I exited for fear of stalling on the freeway. Car has to be towed/repaired at my expense. A friend has the same model vehicle/same problem last year, but due to her car being built at that plant/time was compensated for the same exact problem. Again, Ford is aware of the problem but minimizes coverage. I can't help but think of what could have happened if my wife/daughter had been driving(at night). In reality, it is unsafe and I could have been killed.
Speed shift forced on 2nd and 4th, the vehicle has only 77000 miles and transmission is bad, contacted the dealer about the problem and no action taken, they said the vehicle is not on a recall campaign and owner needed to do repair and if the campaign started on this problem in the future they will reimburse the repair amount, I need the vehicle on a daily basis and now I'm stock with the repairs cost of 1500 plus labor. I need to add this vehicle to the recall as shown here: report receipt date: sep 29, 2015 NHTSA campaign number: 15V606000 component(s): power train the vehicle was in motion when it happened , speed was reduced and wrench light came on the dashboard
Tl* the contact owns a 2008 Mercury Mariner. The contact stated that while driving at various speeds, the cruise control malfunctioned as well as the rpms. The contact stated that the rpms were inconsistent with the actual speed of the vehicle and went up to 4000 rpms at various speeds. In addition, there was a loud clunking noise in the steering wheel and the contact stated that the vehicle downshifted on numerous occasions. The vehicle was not repaired. The manufacturer was made aware of the failure. The failure mileage was 135,000.
In cold weather my gas pedal sticks. Even after I have started my car and let run for 10-15 minutes. When I get in, reverse to forward position and try to accelerate- the gas pedal sticks. I have to slam on it for about 2 minutes before it actually works. This has happened while driving as well, not just the initial start. It definitely happens more in cold weather. What can I do? After research this sounds like it's a common problem with 2008 Mercury mariners. I believe it's definitely a safety issue.
Tl* the contact owns a 2008 Mercury Mariner. While driving 40 MPH, the vehicle hesitated and would not accelerate past 25 MPH. In addition, the vehicle accelerated rapidly without warning. The contact stated that the vehicle shut off on numerous occasions and the check engine indicator illuminated briefly without warning. The vehicle was not repaired the manufacturer was made aware of the failures. The failure mileage was 44,000. Updated 08/04/17
Tl* the contact owns a 2008 Mercury Mariner. The contact stated that while driving and depressing the accelerator pedal, the vehicle would hesitate to accelerate over 15 MPH and the service warning light illuminated. The vehicle was taken to a dealer where it was diagnosed twice that the throttle control module needed to be replaced. The vehicle was not repaired. The manufacturer was notified of the failure. The failure mileage was 96,000.
Tl* the contact owns a 2008 Mercury Mariner. The contact stated that the vehicle lunged forward excessively while attempting to accelerate. The contact engaged her brakes and when releasing the brake pedal the failure recurred. The vehicle was taken to the dealer where the technician was unable to find a failure. No repairs were made to the vehicle. The manufacturer was not made aware of the failure. The failure mileage was 83,000.
I realized sometime last year that my throttle was sticking when I would start the car and begin to take off. It was here and there and then I must have gotten use to it but now it does it even when I'm driving, it sticks all the time. Now it doesn't want to shift at the right times and it acts weird a lot, going up hills, when shifting from gears and so on.
Tl* the contact owns a 2008 Mercury Mariner. While driving approximately 30 MPH, the accelerator pedal assembly fractured without warning. The contact reconnected the arm; however, the failure recurred. The vehicle was not diagnosed or repaired. The manufacturer was notified of the failure. The failure mileage was 80,000.
The throttle is held open when the cruise control is employed but remains open when the cruise control is turned off both by using the off button and brake application. This happens at 75-80 MPH on interstate highways in az and ut. The power brake booster is ineffective with no intake vacuum. This is very dangerous.
Acceleration complaints in other Mariner years
Frequently asked questions
How common are acceleration problems on the 2008 Mercury Mariner?
NHTSA has 31 complaints about the speed control & acceleration of the 2008 Mercury Mariner, 7% of the model year's 461 complaints. The component named most often is accelerator pedal (1 mentions).
Is there a recall for 2008 Mercury Mariner acceleration problems?
No. NHTSA lists no speed control & acceleration recall for the 2008 Mercury Mariner, though it has 3 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 2008 Mercury Mariner acceleration problems start?
Half of the complaints with a recorded mileage happened before about 80,000 miles, and 7% before 25,000 miles.
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.