First lets clear up some misinformation. "I had the check engine light looked at and it is a sensor for fuel/air mix ratio". The closest thing there is to such a sensor is the oxygen sensors in the exhaust system. Those only report the mixture ratio of unburned stuff so the Engine Computer can make adjustments and so it can keep tabs on engine performance. Those sensors report on the result of what has already taken place in the engine. They do not cause misfires or running problems.
The next thing to be aware of is diagnostic fault codes never say to replace a part or that one is bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. In your case, we need the exact fault code number because, assuming it is related to one of the oxygen sensors, there are dozens of fault codes for them, and they mean very different things and have different diagnostic procedures and fixes. Some of the fault codes are set when problems are detected through the readings from properly-working sensors. Replacing the sensors for those things won't solve anything.
The rest of your observations point to a couple of different possibilities. First of all, Ford has had a real lot of problems with steering and suspension parts that can separate leading to loss of control and crashes, so those systems should be inspected at a tire and alignment shop at least once per year, and any time you hear a clunk, squeak, or rattle. In particular, they will look closely at the ball joints, tie rod ends, and control arm bushings. Control arm bushings used to last the life of the vehicle, but in an attempt to achieve a softer ride, all manufacturers are using softer rubber compounds, so now worn and deteriorated bushings are common. Those will not separate and cause a catastrophic failure, but they can cause steering wander and handling problems. A worn bushing will also prevent the wheel from being held in proper alignment, and if bad enough, it can make the tire skid or drag while driving. The clue is you'll be constantly correcting the steering wheel to keep the vehicle going straight.
Your description could also apply to a dragging brake, and there are a few possible causes for that. When you feel the problem occurring, stop on a slight incline, shift to neutral, release the brakes, then observe if the vehicle creeps downhill on its own. If it does not, we will need to pursue the cause of that. Also note that a dragging brake will often cause that wheel to pulse, and since the other one isn't doing the same thing to offset it, you'll feel it in the steering wheel. The second clue is that wheel will feel very hot after driving even a short distance that way. If you have both a dragging brake and some worn suspension parts, you will have very miserable handling. You would have been looking for a solution long before it got to that point.
Thursday, October 6th, 2016 AT 10:23 PM