2003 mercury mountaineer lose power when

It could be a bad temperature sensor producing a false warning. Also, check the oil....sometimes low oil levels could cause the overheat light to come on. Next, have it check out by a mechanic

Tune up,coils wires,fuel filter,dirty throttle body,could be bad cats.

It is hard to diagnose without further information.
This can be linked to engine and/or transmission.
The engine cylinders might lose compression, you might game a leaking motor head gasket, or a fuel delivery problem.

Check for trouble codes.

Possible low fuel pressure or restricted catalytic converter. Have fuel pressure and exhaust back pressure checked.

Click the link below to troubleshoot this problem :---Car loses power while acceleration? http://schematicsdiagram.blogspot.com/2011/12/car-loses-power-while-acceleration.html
----------Loss of acceleration? http://technoanswers.blogspot.in/2012/02/loss-of-acceleration.html
-----------Acceleration lag problem? http://repairhelpcenter.blogspot.com/2012/01/acceleration-lag-problem.html
--------------How exactly the Vehicles Accelerator Cable works?

http://repairhelpcenter.blogspot.com/2011/11/how-exactly-vehicles-accelerator-cable.html

-----------

How exactly Vehicles Accelerator Pump Diaphragm Works? http://repairhelpcenter.blogspot.com/2011/11/how-exactly-vehicles-accelerator-pump.html
----------accelerator pedal sensor? http://technoanswers.blogspot.in/2012/02/2009-chevy-impala-accelerator-pedal.html
----------stalls and bucks on Acceleration? http://technoanswers.blogspot.in/2012/02/nissan-pathfinder-stalls-and-bucks-on.html
---------Engine accelerates when brake is applied? http://technoanswers.blogspot.in/2012/02/engine-accelerates-when-brake-is.html
-----------This will help.Thanks.

Click the link below to troubleshoot this problem: ---
Car loses power while acceleration? http://schematicsdiagram.blogspot.com/2011/12/car-loses-power-while-acceleration.html

----------
Loss of acceleration?

http://technoanswers.blogspot.in/2012/02/loss-of-acceleration.html

-----------
Acceleration lag problem?

http://repairhelpcenter.blogspot.com/2012/01/acceleration-lag-problem.html

--------------
How exactly the Vehicles Accelerator Cable works?

http://repairhelpcenter.blogspot.com/2011/11/how-exactly-vehicles-accelerator-cable.html

-----------

How exactly Vehicles Accelerator Pump Diaphragm Works?

http://repairhelpcenter.blogspot.com/2011/11/how-exactly-vehicles-accelerator-pump.html

----------
accelerator pedal sensor?

http://technoanswers.blogspot.in/2012/02/2009-chevy-impala-accelerator-pedal.html

----------
stalls and bucks on Acceleration?

http://technoanswers.blogspot.in/2012/02/nissan-pathfinder-stalls-and-bucks-on.html

---------
Engine accelerates when brake is applied?

http://technoanswers.blogspot.in/2012/02/engine-accelerates-when-brake-is.html

-----------

This will help.

Thanks.

For acceleration problem, the help links are provided below, click the link below to go through its procedure: ----
Engine accelerates when brake is applied? http://technoanswers.blogspot.in/2012/02/engine-accelerates-when-brake-is.html ---------- Loss of acceleration?

http://technoanswers.blogspot.in/2012/02/loss-of-acceleration.html

----------
How exactly the Vehicles Accelerator Cable works?

http://repairhelpcenter.blogspot.com/2011/11/how-exactly-vehicles-accelerator-cable.html

-------
How exactly Vehicles Accelerator Pump Diaphragm Works?

http://repairhelpcenter.blogspot.com/2011/11/how-exactly-vehicles-accelerator-pump.html

------
accelerator pedal sensor?

http://technoanswers.blogspot.in/2012/02/2009-chevy-impala-accelerator-pedal.html

-------
stalls and bucks on Acceleration?

http://technoanswers.blogspot.in/2012/02/nissan-pathfinder-stalls-and-bucks-on.html

-------
Acceleration lag problem?

http://repairhelpcenter.blogspot.com/2012/01/acceleration-lag-problem.html

-------
Car loses power while acceleration?

http://schematicsdiagram.blogspot.com/2011/12/car-loses-power-while-acceleration.html

---------

This will help.

Thanks.

Normally this kind of a problem is a fuel block...there so many other ways to block...other than the filter

PLEASE don't forget to RATE ME (FIXYA) for my help..........