I installed a Garettson Longneck Intercooler on my '83 930 with the C2 turbo bypass assembly.
The car runs great until the 2-3 shift , that is when it hesitates for a about a second( like you forgot to press the Gaspedal ) then it pulls fine.
I changed the Bypass valve and it did not fix it .
then i reinstalled all the stock intercooler components including the Bypass manifold assembly and the problem was gone.
Any ideas ?