My jump charge script doesn't work. (C#)

So, I am making a controller for a 2d sidescroller. everything works well in my script, apart from my jumping. When I hold down the key, it jumps up and down rapidly. I can't figure out how to fix it. I'll give you the entire code because it has alot of important variables scattered through it; using UnityEngine; using System.Collections;

 public class sideScroller : MonoBehaviour {
     public float maxWalkSpeed = 5f;
     public float walkAcceleration = 0.05f;
     public float maxJumpHeight = 7.5f;
     public float jumpChargeRate = 0.25f;
     float currentWalk = 0f;
     float currentJump = 0f;
     bool ableToJump = false;
     bool hasJumped = false;
 
 
     // FixedUpdate is called once per frame
     void FixedUpdate () {
 
         if(Input.GetKey(KeyCode.D)) {
             currentWalk += walkAcceleration;
             if(currentWalk > maxWalkSpeed || currentWalk > -maxWalkSpeed) {
                 currentWalk = maxWalkSpeed;
             }
             transform.Translate(currentWalk * Time.deltaTime, 0f, 0f);
         } if(!Input.GetKey(KeyCode.D)) {
             currentWalk -= walkAcceleration;
             if(currentWalk < 0 || currentWalk > 0) {
                 currentWalk = 0;
             }
             transform.Translate(currentWalk * Time.deltaTime, 0f, 0f);
 
         }
         if(Input.GetKey(KeyCode.A)) {
             currentWalk -= walkAcceleration;
             if(currentWalk < maxWalkSpeed || currentWalk < -maxWalkSpeed) {
                 currentWalk = maxWalkSpeed;
             }
             transform.Translate(-currentWalk * Time.deltaTime, 0f, 0f);
         } if(!Input.GetKey(KeyCode.D)) {
             currentWalk += walkAcceleration;
             if(currentWalk > 0 || currentWalk < 0) {
                 currentWalk = 0;
             }
             transform.Translate(currentWalk * Time.deltaTime, 0f, 0f);
 
         }        if(Input.GetKeyUp(KeyCode.Space)) {
             print("Jump released.");
             ableToJump = true;
         }
             
         if(ableToJump = true) {
             ableToJump = false;
             transform.Translate(0f, currentJump, 0f);
             currentJump = 0f;
             hasJumped = true;
         }
     }
     void OnCollisionStay (Collision collision) {
         print("Touching world.");
         if(Input.GetKeyDown(KeyCode.Space)) {
             hasJumped = false;
             print("Jump charge started.");
             ableToJump = false;
             currentJump = 0f;
         }if(Input.GetKey(KeyCode.Space)) {
             print("Jump charging.");
             currentJump += jumpChargeRate;
         }if(currentJump > maxJumpHeight){
             currentJump = maxJumpHeight;
         }
 
     }
 }

So, on void Collision stay , it makes sure you cant double jump by having to touch an object to jump. It uses booleans to check if it has jumps and if it can jump. But when it is run, it rapidly bounces up and down. I'm using rigidbody for gravity, but disabling rotation on each axis, and I don't want the motion to be physically accurate so that's fine using transform.Translate. Can you guys tell me what I'm doing wrong? Don't just substitute my script because that isn't very helpful to be fair :) Thanks guys