Need help with flickering and timestep problem in my game

Newbie & Debugging Questions
#1

Hello, I’m new user in this forum but I was reading a lot of threads that helped me but in this case I didn’t get the answer.

My problem is that my game is flickering all the objects (jumping backforward) and I don’t understand why.
I tried to use delta for the movement…, I tried to use sleep…, but nothing works. I don’t know what more to do, and in other tests with delta and “unlimited fps” the code works perfect.
Example of code that works:
[spoiler]http://pastebin.com/vjZ0cgdh[/spoiler]

This is my game loop:

private static void bucleJoc()
	{
		double passat = 0;
		double dividir_entre = 1000.0/60.0;//cada milisegon 
		ultimTemps = lastFrame = Sys.getTime();

		objectes = new ArrayList<ObjecteJoc>();
		jugador = new Jugador(0, ALTURA / 2 - Jugador.ALTURA / 2);
		enemic = new Enemic(AMPLADA - Enemic.AMPLADA, ALTURA / 2 - Jugador.ALTURA / 2);
		pilota = new Pilota(AMPLADA / 2 - Pilota.MIDA / 2, ALTURA / 2 - Pilota.MIDA / 2);
		objectes.add(jugador);
		objectes.add(enemic);
		objectes.add(pilota);
		getDelta();

		while(!Display.isCloseRequested())
		{
			double delta = getDelta();
			passat += delta;

			while(passat >= dividir_entre)
			{
				glClear(GL_COLOR_BUFFER_BIT);
				glLoadIdentity();

				obtindreTecles();
				actualitzar(passat);
				passat = 0;
			}
			renderitzar();
			
			try
			{
				Thread.sleep(2);	
			} catch(InterruptedException e)
			{
				e.printStackTrace();
			}

			actualitzaFPS();
			Display.update();
		}
		tancarTot();
	}

This is my render function:

public void renderitzar()
	{
		crearRectangle(x,y,amplada,altura,cVermell,cVerd,cBlau,rotacio);
	}

	private void crearRectangle(float x, float y, int amplada, int altura, int vermell, int verd, int blau, float rotacio)
	{
		glPushMatrix();
		{
			glColor3ub((byte) vermell, (byte) verd, (byte) blau);

			glTranslatef(x,y,0);

			/*glTranslatef(amplada/2,altura/2,0);
			glRotatef(rotacio,0,0,1);
			glTranslatef(-amplada/2,-altura/2,0);*/

			glBegin(GL_QUADS);
				glVertex2f(0,0);
				glVertex2f(amplada,0);
				glVertex2f(amplada,altura);
				glVertex2f(0,altura);
			glEnd();
		}
		glPopMatrix();
	}

And this my update for the movement:

public void actualitzar(double delta)
	{
		System.out.println("Y: "+ this.y);
		
		if(Keyboard.isKeyDown(Keyboard.KEY_W) || Keyboard.isKeyDown(Keyboard.KEY_UP))
		{
			this.y += VEL * delta;
		}
		if(Keyboard.isKeyDown(Keyboard.KEY_S) || Keyboard.isKeyDown(Keyboard.KEY_DOWN))
		{
			this.y -= VEL * delta;
		}
		//System.out.println(this.y + " " + delta);
		
		
		if(this.y >= Joc.ALTURA - ALTURA / 2)
			this.y = Joc.ALTURA - ALTURA / 2;

		if(this.y <= 0 - ALTURA / 2)
			this.y = -ALTURA / 2;
	}

If you want I can post the full code.
Thanks for the help and attention.