Player Movement Twitching

I'm currently working on a top down game and have come into troubles with my players movement. After I tried to add rotation to my player image he began to twitch quite rapidly as you press the movement keys in game. I was wondering if anyone would know how to fix this so I can have my character face the direction he is moving without all the twitching.

Here is the code for my characters movement:

//Binds keys for player movement
new actionmap(keys);

keys.bindcmd("keyboard","left","moveleft();","stopmoveleft();");
keys.bindcmd("keyboard","right","moveright();","stopmoveright();");
keys.bindcmd("keyboard","up","moveup();","stopmoveup();");
keys.bindcmd("keyboard","down","movedown();","stopmovedown();");

keys.push();


function moveleft()
{
player.moveleft = true;
}

function stopmoveleft()
{
player.moveleft = false;
}

function moveup()
{
player.moveup = true;
}

function stopmoveup()
{
player.moveup = false;
}

function moveright()
{
player.moveright = true;
}

function stopmoveright()
{
player.moveright = false;
}

function movedown()
{
player.movedown = true;
}

function stopmovedown()
{
player.movedown = false;
}

function player::updateHorizontal(%this)
{
if(%this.moveleft)
{
%this.setLinearVelocityX(-40);
%this.setrotation(-90);
}

if(%this.moveRight)
{
%this.setLinearVelocityX(40);
%this.setrotation(90);
}

if(!%this.moveleft && !%this.moveright)
{
%this.setLinearVelocityX(0);
}
}

function player::updateVertical(%this)
{
if(%this.moveup)
{
%this.setLinearVelocityY(-40);
%this.setrotation(0);
}

if(%this.movedown)
{
%this.setLinearVelocityY(40);
%this.setrotation(180);
}

if(!%this.moveup && !%this.movedown)
{
%this.setLinearVelocityY(0);
}
}

function SceneGraph::onUpdateScene()
{
if (isObject(player))
{
player.updateMovement();
}
}

function player::updateMovement(%this)
{
%this.updateHorizontal();
%this.updateVertical();
}

//makes camera follow player
function player::onLevelLoaded()
{
%force = 20;
%keyforce = 0;
scenewindow2d.mount(player, "0 0", %force, 1);
player.lives = 3;
}



This is the code I tried to add to stop the twitching because I thought it might be caused by the constant updating of the players rotation and I don't understand why it doesn't work.



function player::updateHorizontal(%this)
{
if(%this.moveleft)
{
%this.setLinearVelocityX(-40);
if(%this.getrotation != -90)
{
%this.setrotation(-90);
}
}

If someone could help me out that would be awesome.

Thanks,
Josh