2003 merc. mountaineer with v-8, has a miss, service eng. light o

Clean the Throttle Body and Mass Air Flow Sensor. Also check for DTCs (diagnostic trouble codes).

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What are the codes

Sounds like a coil breaking down. Try this for a test, get going to around 45 mph and lightly accelerate, is the is miss is reproduced then the most likely cause is the secondary ignition system. I.E plugs or wires or a coil.

I have a 2003 ford windstar.Engine started to run rough when it
used to rained.I would accelarate it until roughness would go away sort of.It lack a little power but if I take it a mechanic they would charged too much money.Anyway, the problem was a spark plug wire in front of the engine, wires that are grouped together with that little pin. One of them was rubbing agains the valve cover and it got worned out current would leak out right there.I discovery it one time that it rainned really hard I had to go out and the wagon started to miss really bad and it wouldn't move.Finally, I got home the next day I looked under the hood to see what I can see and there it was a spark plug wire that one can tell if you know a little bit about cars that current was leaking throw it. I replaced wire problem solved.But now after all of that snow we had the check engine light came on and I am not sure what could be.For I remmerber running over a mountain of sort of hard snow.So it probably broke oxigine sensor wire.

Is the car missing or not running quite right, have a little more wiggle to it? Flashing check engine light is usually indications of a cylinder misfiring which could be caused by a few different things.

Check the EGR valve. Look up on the internet where on your car it is located. Find the vacuum line connected to it. Start the engine cold and as it warms up and starts to miss and stumble, pull off the vacuum line from the EGR. If the car idles fine, replace the EGR. Ignition system problems are more likely to occur at idle or lower rpm. Besides, testing the EGR is free, easy and do fail in high mileage vehicles.

Could be a defective fuel cap, or you just need to take the cap off and put it back on.

Sounds like you need to service your carb as the mainjet is probably partially blocked or you have a choke thats not opening properly or a blocked filter.

This could be a number of things causing this ...most common is that after you fill up the gas cap is not fully tightened...make sure it "clicks" 3 times while turning.The other common problem is that the gasket on the gas cap is old and thus does not seal the tank/fuel filler area...check with replacing the cap.If neither correct then you will need to bring to a service center or dealer to run a code check...maybe a bad O2 sensor or a code for the transmission.

Have you used a NOID light to see if injector is getting a signal, the NOID lite is a little test tool that plugs in the injector connector and flashes when eng is running is signal is present, a vacuum leak can cause this as well, also the injector can be faulty, check the compression 1st, then do the other tests, I was a dealer tech so I had access to a piece of test equip called a SBDS, it could quickly give me all the info about the miss-fire, most case knew the problem in 10 minutes, of course the machine cost $75,000 so in a independent shop it is out of the question. Good Luck