yes that is true it happen on my moms 940 turbo on my car it was an early stage my engine wouldn't idle right it idles better now but I still have some surging any Idea's it's not the 02 or the amm as far as I know a word of wisdom for you when or if your going to emabark on this task two things happen to me that slowed me down 1. the studes in your turbo that conects it to the down pipe are more or less part of the turbo now so if you brake them make sure you have a machine shop to take the trubo to. 2. if your going to do the job right you should replace every seal possible in that area as well as replacing the turbo lines. I did oil cooler, all turbo lines, exhaust and oil cooler lines. also when putting it all back together make sure the first thing you put in is the line that leads up from the engine block to the bottom of the turbo assuming you have a garrett turbo. It will not fit in other wise.I had to heat up the pipe bend it then bend it back while it was on the turbo. that sucked

Good luck and good fixing