I have a 2004 focus that runs pretty good when idling but as soon as you put it i gear it shakes bad. when you turn the ac on it tries to die. There is no check engine light on.The plugs look really lean. I have 40 pounds of fuel pressure and it holds for 30 mins after turning the car off so i dont think thats it. Im sure a sensor is causing the problem by not reading right but i cant seem to track it down. thanks in advance for any help.