Custom Spring acceleration neverending increasing

Hi everyone,
I'm trying to make a simple spring algorithm between 2 objects, the formula is quite simple.
But the acceleration and speed of my 2 objects don't stop increasing as if energy was constantly added.
What's wrong with my approach?

Code (CSharp):

1. Spring = 0.5
2. Damping = 1
3. FixedDist = 2;
4.  
5. for each object in Update, I do :
6.  
7.            // Get Distance.
8.            Vector3 delta = (this.transform.position - other.transform.position);
9.            float distance = delta.magnitude;
10.  
11.            // Get Force.
12.            Force = -Spring * (distance - FixedDist) * delta / distance - Damping * (this.Speed - other.Speed);
13.  
14. for each object in LateUpdate, I do :
15.            Accel += Force / Mass;
16.            Speed += Accel * Time.deltaTime;
17.            transform.position += Speed * Time.deltaTime;
18.  

 

ok,
I think I have my answer.
I have to add some drag factor on accel and velocity at each update.