Timing could be slightly out
this would cause rough running & low power
& if the advance solenoid is broken
it wont run right anyway

an easy way to check if the solenoid is working is to listen for a ticking sound before you start it
it will tick fast for a few seconds
once ignition is on

theres a few things that could cause low power
could be something simple like blocked catalytic converter

Could have restrictive air flow due to dirty air filter etc
id try taking air filter out & go for a run if that dont make no difference
id drop the downpipe off the turbo to eliminate exhaust blockage
other than this id be checking timing etc
start from.basics that you can eliminate yourself before going to a garage

but as i said before if the advance actuator isnt working it wont run right & will be rough.
Struggle to start & low on power

hope this helps ya