v6 engine problem
 

my girlfriend has 97 mustang with a 3.8 v6 and automatic. the car has a shudder in it when it idles down. it occurs between 1100 and 1000 rpm. it also does when your driving at a steady speed and you barely give it throttle. You can feel a shake in the engine and it comes and goes. if anyone has any ideas what it could be i would sure appreciate your time .
thanks
eric

oh by the way what is the throttle position sensor voltage suppose to be at idle

I think you may be onto something with the throttle position sensor. There is an easy way to test the sensor. Disconnect the sensor from the wiring harness. Attach the negative wire of a multimeter on the center pin of the connector and the positive wire on the hot pin of the connector. I'm not sure of the color coding of the hot wire, but if there is a solid black wire, it's the ground; use the other one.

What you are measuring is the resistance in the sensor. As the throttle is pressed, the resistance reduces to 0 which indicates WOT(wide open throttle). While testing, the resistance level should smoothly decrease as you press the throttle. Test completely through the throttle range, you may find more than one bad spot.

I suspect you will see a jump(s) in resistance when you perform this test. If you do, replace the throttle position sensor. This will cause all of the symptoms you have described.

Ususally the voltage to the TPS is 12 volts, but this isn't what the sensor is modifying when it's working. The car provides ungrounded voltage to the sensor which provides more ground (through less resistance).