1. Locate the throttle pedal spring. It is located under the pedal, attached to the throttle linkage.
2. Disconnect the throttle linkage. There is a small cotter pin that holds the linkage in place. Remove the cotter pin and then pull the linkage off of the pedal.
3. Remove the old spring. There are two bolts that hold the spring in place. Remove the bolts and then lift the spring out.
4. Install the new spring. Place the new spring in position and then insert the two bolts. Tighten the bolts until they are snug.
5. Reconnect the throttle linkage. Push the linkage onto the pedal and then insert the cotter pin.
6. Test the throttle pedal. Make sure that the pedal moves smoothly and that there is no binding.
That is how you change a throttle pedal spring on a 1991 Peterbilt.
