It is a strange problem because 1,1,2,2-tetrachloroethane usually doesn't fail the minimum response factor. I would suggest to try a new trap if you haven't done so.

This may sound silly, but make sure you have the right concentrations for the internal standard and 1,1,2,2-tca in the calibration table and you are using the correct ions for quantitation.

I doubt split ratio will help the situation because the split ratio won't change the mass ratio of internal standard and target compound injecting into the column.