My dads truck has a problem with the check engine light coming on. It's been to a few mechanics and a ford dealer and no one can figure it out. when its raining out the check engine light will go out and come on. when he comes to a stop sign sometimes the engine wants to bog down and die and sometimes it wants to rev up and take off. It sounds to me like a sensor on the intake side of the engine. any ideas? Also it won't go into 4 low.