'87 5KTQ performance trouble

[Colin Hames <cchames@mm.com>]

Everyone,

        Looking for some answers regarding my '87 5TKQ (150,000
miles).   I am currently experiencing some driveability/performance
troubles that
myself and the dealer have been unable to resolve.  
        My first problem is the car starts to stumble about a minute
after a cold start.  This continues until it is fully warmed up.  Even
after is warms up there is very mild surging at partial throttle.  I
have tried a warm regulator from '88 5KT that is running fine and that
didn't help.  
        Second,  the car very rarely  exceeds 1.2 bar of boost.  Once in
a while it seems to run great (1.4 bar I think is normal) only to return
to it's pokey state after a couple miles or after restarting the car.
The throttle switch and ECU have been replaced and also various breather
hoses so there shouldn't be any vacuum problems.
        Occasionally the check engine code 2141 for knock sensing comes
on.  I have tried all grades of fuel so I don't know what to think
there.
        I have experimented briefly ( and carefully ) with bypassing the
wastegate solenoid.  As expected boost pressures came up quick and
smooth with the ECU stepping in to shut off fuel.  Seems the wastegate
and turbo itself are fine.
        
Thanks for any input,

Colin