The throttle valve cable controls the air and fuel that flows into the engine. It meters the fuel that mixes with outside air by opening a valve--the throttle--which is a plate that opens and closes inside the throttle body. When the plate opens, air is drawn in by vacuum pressure created by the design of the throttle body. Vacuum pressure also draws in fuel which is then sent to the engine's combustion chamber. If your throttle valve cable is not adjusted properly, however, you will experience either a fast idle (decreasing fuel efficiency) or a slow idle (potentially causing the vehicle to stall). To fix this, you'll need to know how to adjust a throttle valve cable.
Locate the throttle body in your vehicle. In most cases this is a rectangular object that sits near the firewall in the engine bay.
Turn the throttle adjustment bolt(s) clockwise to tighten and counterclockwise to loosen. The exact location of the adjustment bolt will vary with your vehicle, though it is usually located near the throttle body itself. Depending on whether you are experiencing a fast idle or a slow idle, you'll need to tighten or loosen the throttle valve cable.
Check the tension on the throttle valve cable once you're done adjusting the cable. For many vehicles, there should be approximately 1/4 inch play in the cable, though you should refer to your specific vehicle manufacturer's service manual for the exact tension specifications.
