D5 engine defective?

Hello, since my C70 II has been running mostly impeccable so far, this is my first visit to your forum! He has now run 260,000. I had a failure of my air conditioning system about 3 years ago (no longer cooled) and have not yet had it repaired for cost reasons. After that he showed me the engine maintenance warning, did not put on properly and I left with my screwdriver which is not a Volvo workshop but one of the typical cheaper allrounder, that check. Fault memory probably showed something with the throttle flaps at the time, so they were replaced (my workshop probably took some help from a Volvo workshop for). Then it was a long time again. In between I was at a Volvo dealer, because I do the inspections alternately at a Volvo workshop, sometimes at my screwdriver. This told me when I told him about the story that this error message was possibly wrong and by the Fe I think Fuchs ik listen to you and didn’t react very quickly. Sometime later, however, he finds again to have no power. It is so that he pulls in cold the first 4 minutes or like a 40 HP car, after that it gets better but not the level that he should have. I was b an error message is no longer there but the limp performance is unchanged. Now I’m thinking about whether I should go to the Volvo workshop or to my screwdriver – what do you mean what is defective and how expensive this is going to be? I want to drive the car, which has experienced many of its kilometers on highways in its first 5 years, actually for many years and therefore not to repel it. But I want to d don’t pay 2,500,- where maybe a repair even only 1,000,- must cost if you know inn about what it is… Thank you in advance for your help !