where is the problem: Residuals are oscilating
 

hi everybody

I have a problem with my residuals. I added the temperature with Boussinesq assumption to viscoelasticFluidFoam solver and when I ran it the 'tau' residuals are oscillating and the interesting point is that it is ahead of the rest!!!!
I've attach the residuals plot.

any body knows where is the problem?

thatks
Mostafa