Ah, good to hear from you, Simon. I was hoping you'd report back.
How long have you had the TB and plugs installed? the exhaust is a good sign - has it changed smell as well? what about the moisture content, does that seem increased?
now, to your question about mileage gains: you've undoubtedly heard the old saying "with great power comes great responsibility."
that means that just because you have access to it, doesn't mean you should use it. like nuclear weapons.
Your mileage gains will kick in when you take that perspective to your accelerator pedal, consistently and diligently. (staying out of turbo range would be a good start...you SHOULD find you may not need it as often as in the past) That said, if you've not seen even a slight improvement yet, there may be other issues that need resolving, or you may need to make other additions to the car to take advantage of what's now happening in your intake manifold and cylinders. I can't recall anyone reporting a grooved Volvo here before, so you might be a test case. It might be that a traction control computer is foiling gains...and I just had a thought: you didn't mention completing the drive cycle when you had the Throttle and plugs installed. Did you follow the directions Ron Included in your package? The computer(s) have to be given the chance to adjust, and you do have to point them in the right direction. (if this install happened while fuel refineries were changing their formulations from summer gas to winter gas, your machine is trying to sort out it's baseline while adjusting to a change in fuelling)
You may need to Add EFIE circuits to your oxygen sensors to help the computer along...and if you do that, provided it might prove necessary to do so, you'll also need to take a look at the MAP sensor (assuming you have one, which I'm assuming you do for fuel delivery/timing when the turbo kicks in) and how to modify that circuit. the Groove HAS changed the dynamics of the intake manifold, after all, so that sensor and how the computer sees the signal from it and its reaction to that signal may have a more profound effect than you may currently consider.
I truly hope that this doesn't seem too much bother to you, but while the groove is a miracle (my opinion and experience with it), the results don't always happen just by swapping in a few parts; so far you seem to have been a thoughtful, intelligent, purposeful man and I hope you decide we can work together to determine how to make your Volvo less thirsty.
