Cat 315 left track moving by itself

I have a caterpillar 315 excavator that the left track moves without me stepping on pedal. As soon as I move the unlock stick the machines left track moves backward with me stepping on pedal. I removed the lower cover it see if there was An adjustment and I don't see any. If I put pressure on the pedal forward the track stops moving. Is there an adjustment I am not seeing or is that pedal valve sticking or maybe something else. Anyone have any ideas. Please help. Thanks

Cat 315 left track moving by itself