Petrol Turbo will NOT increase MPG!!!!
How can you get more power like this? Yes they run 'lean' as standard - you should purchase VCDS and 'log' this 1.8T fuelling (if you can - these are not all wideband), then monitor fuelling with remap and see what happens.
Speaking of turbo diesel - when you mess with 'rail pressure' (which I am personally against), or adjust 'injection duration' map(s) the MPG display will be even more out of sync than the original software. The little display on instrument cluster is just a guide, it guesses, and constantly changes because it is just a toy.
For real world MPG test please fill your tank to the brim 3-4 times and reset the 'trip' counter. Do the same after remapping and see what MPG you really get. For mature drivers they stay around the same - to make a Turbo Diesel quicker we use more fuel. Smoke should not happen IMO, it is too much fuel (I would pull back slightly at higher RPM for the person with smoke there - but depends on the customer/their budget etc).
With petrol turbo - you cannot expect to tune for more power and not see increase in fuel consumption.
Most throttle (fuel) LAMFA request lambda 1 in these 1.8T (14.7.1 AFR <-- very LEAN for petrol turbo, but working 100% from factory). After this we have 'actual' fuel KFLBTS lambda for component protection (if 'throttle' request is not good enough, different engine conditions) dropping very low maybe lambda 0.7 (10.2-10.4 AFR <-- TOO RICH FOR THESE ENGINE!! But manufacturer do for protection)
Try to think at 100% throttle, most of these petrol turbo are requesting 14.7.1 AFR. Very lean! You cannot modify this engine without REDUCING lambda, which INCREASES fuel!!!
Lambda 1.0 = 14.7.1 AFR (some say 'optimal' for engine power/torque under certain conditions)
Lambda 0.9 = 13.2 AFR
Lambda 0.8 = 12.2 AFR
Lambda 0.7 = 10.2 AFR (too much fuel in 'some' engine and lose power)
Who is promoting MPG increase on engine? The day I see an 'economical' remap that is true, I will donate my programming tools to charity and become a prostitute.
I attach 2.0TFSI K03 197hp 'log' with modify software ONLY, no engine mods. Ignore 'specified' fuel look at 'actual' fuel to see where 0.828 lambda, shows 0.83 from 4000RPM to redline, 100% working, 100% good enigne. You will notice load request very 'close' to actual, with boost very close to request! I can reduce LDRXN (load limiting) from 4000RPM upwards because the engine is not giving as much here you see