Low RPM

My 2003 Astra SXI DTI has been stationary for 12 months. I took it for an MOT today, it passed but… the RPM will not go above 3000. During the MOT it spewed out black smoke. I tried the same while moving, put it in neutral and hit accelerator. No black smoke but would not go above 3000 RPM. I read somewere it is either moisture in the CPU and would fix itself if I take it on a long journey, or the turbo has packed up… I’m praying that it is the moisture theory as I immagine a new turbo would be expensive. What do you guys think…?

What’s a MOT

Ministry of Transport test… a compulsory roadworthynes test carried out annually on all vehicles over 3 years old in the UK…

It’s not getting enough air I think.
Check the air filter.
Could be the turbo isn’t spinning. May need no more than reaching the rotor and giving it a nudge to free it up.
Where is the computer located?