I have a Mercury Mountaineer 2002 is Bucking stalling really bad once in awhile it will stop and run great for a day and then do it again can you please help me

Engine light on? If so, have it scanned for free at Auto Zone. Get codes only. Sounds like you cat. converters are stopped up. When this happens the engine can't breathe so it shuts down.

Is the check engine light on? Mountaineers are bad about developing vacuum leaks which will lean the engine out and cause it to stumble at idle while in gear. Check for p0171 and p0174 codes.

013 Idle Speed Problems PCM Test

007 Idle Speed Problems Scan Data for Idle

test don't guess .

Check the fuel pressure with a gauge. The pump may be going bad

try to replace the fuel filter that may help

I think you should go for manual first after that it will be easy for u to solve your problem. I had visited this site past 2 months before for my vehicle and find it quite helpful may be you will also get something useful here
Mercury Mountaineer 2002 2005 Factory Service SHop repair manual Download

Yes Brother, I know that experience. Have a computer test done to find which cylinder is misfiring and replace that fuel injector. It's gone dead and we call this a dead cylinder. Seems like it runs fine, until you hit overdrive. Then it feels like you're running on one square wheel. A steady thump.

timing belt idel spring could be bad

Hi, maybe there's a problem in your starter or your battery consume more electricity.

NephetZ

check the fuel regulator,while running unplug the red vacumn hose and if gas squirts out the hole,then it is bad,if not then possibly plugged catalytic converters,drive it on the highway if you can, and stop and look underneath at it and if it looks red,then replace them.Check to see if its overheating,usually a really hot hood tells the story.