Need help with player movement,Help with character controller

Hi I'm in the early stages of working on a game and I am having some problems getting my player movements to work properly, so I thought I might try my luck and see if anybody in here would be able to help me.

The problems I have is that I have made a statemachine to keep track of my states and rules for switching between them which seemed to work in the beginning but I can't seem to figure out the code to switch from walk to idle, fall to idle and fall to walk. If I try to add code to switch to idle when the player isn't moving I won't be able to walk at all since as as soon as I try to walk the state will immediately go back to idle, on the other hand if i jump as soon as i touch ground the player just stand still and I have to release my walk button and press it again to resume walking.

Below is the code I'm working on.

StateMachine.cs:

 public interface IState
 {
     void Enter();
     void Execute();
     void ExecutePhysics();
     void Exit();
 }
 
 public interface StateManaged
 {
     void RequestState(IState requestedState);
 }
 
 public class StateMachine
 {
     public IState currentState;
 
     public void ChangeState(IState newState)
     {
         if (currentState != null)
             currentState.Exit();
 
         currentState = newState;
         currentState.Enter();
     }
 
     public void Update()
     {
         if (currentState != null)
             currentState.Execute();
     }
 
     public void FixedUpdate()
     {
         if (currentState != null)
             currentState.ExecutePhysics();
     }
 } 

PlayerController.cs

 public class PlayerController : MonoBehaviour, StateManaged
 {
     StateMachine stateMachine = new StateMachine();
 
     public float speed = 5.0f;
     public float jump = 20.0f;
     bool isGrounded = true;
 
     private Rigidbody playerRigidbody;
 
     private void Awake()
     {
         playerRigidbody = GetComponent<Rigidbody>();
     }
 
     void Start()
     {
         RequestState(new IdleState(this));
     }
 
     void Update()
     {
         Debug.Log(stateMachine.currentState);
         CaptureInput();
 
         stateMachine.Update();
     }
 
     void FixedUpdate()
     {
         UpdateStateFromPhysics();
 
         stateMachine.FixedUpdate();
     }
 
     private void CaptureInput()
     {
         if (Input.GetKeyDown(KeyCode.A) || Input.GetKeyDown(KeyCode.W) || Input.GetKeyDown(KeyCode.S) || Input.GetKeyDown(KeyCode.D))
             RequestState(new WalkState(this));
         
 
         if (Input.GetButtonDown("Jump"))
             RequestState(new JumpState(this));
     }
 
     private void UpdateStateFromPhysics()
     {
         if (playerRigidbody.velocity.y < -.01 && !isGrounded)
             RequestState(new FallState(this));       
     }
 
     #region
 
     // Manage state transition rules
     public void RequestState(IState requestedState)
     {
         Debug.Log(requestedState.ToString());
 
         // Idle
         if (requestedState is IdleState)
         {
             if (stateMachine.currentState is null || stateMachine.currentState is WalkState || stateMachine.currentState is FallState)
                 stateMachine.ChangeState(requestedState);
         }
 
         // Walk
         if (requestedState is WalkState)
         {
             if (stateMachine.currentState is IdleState || stateMachine.currentState is FallState)
                 stateMachine.ChangeState(requestedState);
         }
 
         // Jump
         if (requestedState is JumpState)
         {
             if (stateMachine.currentState is IdleState || stateMachine.currentState is WalkState)
                 stateMachine.ChangeState(requestedState);
         }
 
         // Fall
         if (requestedState is FallState)
             if (stateMachine.currentState is JumpState || stateMachine.currentState is WalkState)
                 stateMachine.ChangeState(requestedState);
     }
 
     public class IdleState : IState
     {
         PlayerController player;
 
         public IdleState(PlayerController player)
         {
             this.player = player;
         }
 
         public void Enter()
         {
 
         }
 
         public void Execute()
         {
 
         }
 
         public void ExecutePhysics()
         {
 
         }
 
         public void Exit()
         {
 
         }
     }
 
     public class WalkState : IState
     {
         PlayerController player;
 
         public WalkState(PlayerController player)
         {
             this.player = player;
         }
 
         public void Enter()
         {
 
         }
 
         public void Execute()
         {
             Vector3 movement = new Vector3(Input.GetAxis("Horizontal") * player.speed, 0f, Input.GetAxis("Vertical") * player.speed);
             player.playerRigidbody.transform.position += movement * Time.deltaTime;
         }
 
         public void ExecutePhysics()
         {
             
         }
 
         public void Exit()
         {
 
         }
     }
 
     public class JumpState : IState
     {
         PlayerController player;
 
         public JumpState(PlayerController player)
         {
             this.player = player;
         }
 
         public void Enter()
         {
             Vector3 jumping = new Vector3(0, player.jump, 0);
             player.playerRigidbody.AddForce(jumping, ForceMode.Impulse);
         }
 
         public void Execute()
         {
 
         }
 
         public void ExecutePhysics()
         {
 
         }
 
         public void Exit()
         {
 
         }
     }
 
     public class FallState : IState
     {
         PlayerController player;
 
         public FallState(PlayerController player)
         {
             this.player = player;
         }
 
         public void Enter()
         {
             
         }
 
         public void Execute()
         {
 
         }
 
         public void ExecutePhysics()
         {
 
         }
 
         public void Exit()
         {
 
         }
     }
     #endregion
 }