Hello fellow Volvo owners. I'm hoping someone can point me in the right direction and help me troubleshoot this issue. I'll do my best to describe what has been happening, but I may get some of the jargon or names wrong for things. Pleas bear with me and feel free to ask as many questions as you like. I will do my best to answer them.
The yellow engine warning light came on and I took it down to a local mechanic who scanned it and told me it reported something to do with the anti-pollution system. I was about to take it away for a longish drive on holiday, so he recommended I bring it back to have a look at it after that and assured me that it wasn't a serious issue. He suggested using Mobil Diesel and he cleared the yellow light on the computer system.
[I should note at this point, I'd previously had the hoses on the gearbox (vacuum?) replaced as there was a reluctance for the vehicle to change gear at the right time. After this repair but before I went away I did notice that there was a slight over revving happening on occasion but I had put this down to the gearbox that had just been repaired and I thought it could be related. Which was what I asked the mechanic to check - just in case a hose had come loose/not been fitted correctly etc.]
So after a couple of days and some decent freeway and open road driving the light came back on. I couldn't really tell any difference in performance at the time it came back on. A couple of times during my trip I had some quite weird engine feedback. I was feeling like there was about half of the power that should be available. Foot flat down and running at highish revs the engine just wasn't giving much at all. At one point it laboured up a hill at 50km/h with the foot down flat on the accelerator and revving to around 3500-4000. Normally I would expect to cruise up that hill at around 80km/h with around 2000-2500 revs. This happened only about 2 or 3 times during a 10 day trip.
Since then the engine light has turned off of its own account and the problem hasn't arisen again.
(Edited to correct the rev numbers, I had initially overestimated them).