I have a 2008 Taurus. I am very happy with my car, and it has over 200k miles, but I have had a small problem with it for a while now. I did not change the spark plugs until about 120k miles. At that time, when I was driving uphill on the highway and before the transmission downshifts, I would sometimes get a skip/misfire (sort of the car bucks) in the engine. I found that if I put super unleaded gas in the car then it happens much less frequently. Maybe I waited too long to change the spark plugs and did some other small damage to the car to cause this. It continues even after changing the spark plugs.

When I tell the dealership, they don't really know what to say and they suggest fuel system cleaner. That doesn't help.

I found this link online and this seems to be exactly what I am seeing:

Engine Buck/Misfire at Freeway Speeds : Ford Taurus Engine

Has anyone had this happen to them? Does this sound right? Is this a big repair?

Any input on this is appreciated.

 

Usually a bucking sensation is due to loss of ignition system function. Something like battery cable connections, coil condition, and yes poor quality fuel (contaminated with water) or even temporary fuel supply interruption can produce these symptoms. Consider having the vehicle checked for any codes in the computer which could provide some direction with an intermittent problem.

 

Here is an update. I brought my car to my local dealership and they first looked at the service bulletin that I mentioned before, but they said that it doesn't apply to my car (it is for another engine I think they said). Then they took my car for a test drive with a laptop connected to it to help diagnose what is happening. They were able to see that one cylinder was misfiring. When they opened up under the hood they saw that there was some oil inside where the spark plugs are. The interior valve cover gasket apparently was leaking and oil was fouling the spark plugs. I remember the last time that I changed the spark plugs, the mechanic told me that the plugs were in bad shape and looked like they were oil fouled. Maybe they should have noticed this then. Anyway, for now they changed the valve cover gasket, the spark plugs, and with the mileage that this car has, they changed the rear ignition coils (the rear ones are hard to get too, so as long as everything was being taken out for the other work, it made sense to do). The total cost was about $1400 but it seems to have fixed the problem, so I am happy.