Engine: D5: V70 very inter power loss cured !!

[DanielHoward]

I have had this Volvo S60 D5 for three years now. Recently, there was some strange set of noises in the cabin when I accelerated like the engine no longer singed or was noisier. I filled the tank with good diesel from BP (the more expensive diesel) and put Redex. Did this twice. I put some additive into the oil that reduces noise (maybe that was unwise but perhaps unrelated). After two weeks one fateful day one week ago the engine sounded great, the noise had gone, and it had very good acceleration as usual. I was happy. Next day I got in the car and started driving. Suddenly it drove like a 1 litre car not a 2.4 litre car!!! it had no power particularly uphill and coincidentally or not a message appeared "Engine Service Required". Over the next two days the problem remained but it was more or less manifest. In one instance I was going uphill and felt as though the guy behind would blow the horn for I could not accelerate. In all cases the revs go up but the acceleration is not there. During those two days I took it to one garage to read the code (a "friend"). He charged me 20 pounds although the young kid who worked for him saw no associated error code. Today I went to another mechanic friend who is more experienced. I brought a fuel filter to him (for I heard this may be a reason). He changed it. We checked the hoses to the turbo and revved the car and they had pressure in them so we realized the turbo was right. We checked everywhere for leaks and found none. However, we did hear a strange noise from the stepper motor, something unusual. I took the car for a long spin. The engine sounded much better with the new fuel filter. However, the problem with power remained. Say on a motorway it took a long time to reach 70 mph and uphill or downhill even slightly on roads makes a big difference to the car. You get the impression you are not pressing the accelerator but you are flooring it but the speed wont pick up. My friend thinks it is the throttle housing area, something sending the wrong air or something to the engine. Moreover another friend thinks it may have to do with particulate filters but I don't know. Also this mechanic who changed the fuel filter tried with his limited OBD and was able to reset the message of normal service required (that message was showing also) but not the "Engine Service Required" message, he could not turn it off nor could he read the code, there was no associated error code to point to the fault. On Tuesday I am going to a Bosch Service Centre for they have more powerful diagnostic computers. If that fails I will go to the dealer to try to get the diagnostics. Does anyone have any theory as to where might the fault lie?