The front shocks are so easy to do. When I did mine I didn't even disconnect the bottom ball joint.
If you can hire a spring compressor, you can do the job yourself, but if you have to pay then a professional worth his salt shoud take no more than 90 minutes. Allow thrity minutes for the sorry guv, the strut cap was a bit rusted on, and you should pay two hours labour plus parts tops.
The exhaust emission is a tougher one to explain. If the level of unburnt hydrocarbons is too high it could be that the mixture is too lean for full combustuion, or too rich. Also worn piston rings can lead to a higher reading due to the burning of oil. A sound 924 engine is easily capable of bettering the exhaust emission regulations for a vehicle for that year of manufacture. If the mixture is in need of adjustment, the guy who does the shocks should throw in the mixture adjustment for nothing as it takes no time at all to insert a 3mm allen key into the little tubular hole in the metering unit between the metering head and the rubber duct flange, and moving it perhaps a 16th of a turn lean (anti clock) or rich.
