I have a 2000 mercury sable and after a fill up one day the car started idling rough especially when I was stopped at a stoplight, etc.. thought I had bad gas...added water remover....well apparently that is not it. I also added fuel injector cleaner. The car exhilarates by itself, my rpm tack races up and down, eating gas like crazy, cant idle in drive without dying, when I approach a stop I put car in neutral so it wont die. Now as of last nite it is making noises...never seen a car exhilarate on its own without foot on gas????

SOURCE: My 1997 Mercury Mystique dies

Check the AIS (idle speed motor) the bypass passage may be clogged with crankcase vent sludge. This is a problem I found many vehicles

SOURCE: rough idle

Mercury had a recall on 3.0 duratech motors in 2000 and 2001. If you get a fuel smell at startup then you might have a bad lower intake gasket, it could cause a miss if seal is cracked. Article No. 01-4-3 you can get it on AllData.

Also, check the PC rubber L piece that runs from the PVC valve to under the throttle control - it could be busted.

Make sure ignition wires are not cracked. If you haven't tuned it up in over 30-40K consider doing that.

SOURCE: 1989 Mercury Sable GS 3.0L runs rough and idles down and stalls

Sounds like you might have a stuck open EGR valve. Is the check engine light on. I would replace the fuel filter if it hasn't been replaced, also check the air filter.

SOURCE: 1993 Mecury Capri Timing Belt? Fuel Injectors?

If it runs better at times, then it sounds like a sensor. The ECT could be bad, it can cause idling and power issues.If the check engine light is flashing, then that can also be researched...blueamber...I've owned 6 of these capris so far