[Stan22]

I only replaced the spark plugs (car was working fine before). Now when the car is idle the speed goes up and down and eventually turns off. The car works fine when driving at higher speeds. I also replaced the wires thinking it was that. I cleaned the air mass sensor, thinking it was dirty, and then even tried putting a new one in and still nothing. I triple checked the spark plugs, they are in (also put the old ones in and the same thing is happening). I also triple checked the spark plug wires to make sure they are going to the right ones. Please help!!

It's a Mercury Cougar 1999

 

[r-clar]

Sounds like you may have a large vacuum leak. Are you sure you got the intake on right and everything hooked up properly?assuming it's a v6

 

[amc49]

Late, but if the plug wires were not new then often yanking them makes them go bad as the conductor inside is only carbon impregnated string. The physical action of pulling on the wire often separates them inside where you can't see it. Much easier to do that on old wires.