if the tps sensor or cam sensors were faulty, it would bring the engine warning lamp on. if the tps fails, it has two sensors in one due to the drive by wire (it must constantly compare one to the other for fault tolerance and safety) nature of the car the car will go into limp mode and not rev/run rough but allow the car to to be moved off the road. it uses this sensor to determine the electric throttle motor position, any minor fault here and you will know it. if either of the cam sensors fail (has 2, one for each camshaft), it will bring the engine light on, but still run ok, because it will use the other cam sensor, should not effect fuel economy much if at all because it wasn't until the later models such as BF that the vct cam actuation became independantly variable. sounds like you have a bit of a problem child of a car to be honest. my advise would be, make sure the car ecu has the latest firmware flashed into it, there may be a tech bulletin related to the issue, but surely ford should have checked this out when they inspected it? otherwise, changing spark plugs and oxygen sensor can never do any harm and I would suggest these to anyone that is having problems related to economy, even if they seem ok. could always be a mechanical energy loss issue associated with the gearbox that may not be locking up the torque convertor and causing bad economy or faulty convertor that is slipping due to incorrect transmission fluid, the transmission also has a internal fluid temp sensor that changes the shifting operation, if this sensor was reporting to the ecu that it was cold all the time and not locking the torque convertor up it will waste fuel and not set an engine light, because the reading is in spec, just reporting incorrect temp reading, these types of things are improbable, but never impossible either. just trying to think out the box a little because it sounds you are running out of options.
