Surely if the light is on there must be a fault code? Have you give it chance to log a code by ignition cycle on/run/off a few times?
Assume this is on the Octavia VRS?
To see if it's mapped,one test, is to do a vag-com/vcds MAF airflow test on the live data measuring blocks.
You can
roughly work out the bhp from the airflow. (providing the MAF is good)
http://wiki.ross-tech.com/wiki/index.php/Fuel_Trim_Info
Here's a good sanity check for the status of your MAF. Do a full-throttle run all the way to redline in a single gear (second works fine). Group 002 usually shows air mass in g/s (in many modern ECU's, consult your Factory Repair Manual for the specific group for your particular vehicle). Your peak airflow should be roughly 0.80 times your horsepower if you are close to sea level. So, if you have a stock 150 hp 1.8T, expect around 120 g/s. If you see significantly less than that, you MAF may be on the way out. Also note that airflow will be markedly different at higher altitudes due to reduced ambient air pressure, especially with naturally aspirated engines that do not have forced induction to overcome that deficiency. This still works if you are chipped, but "race" programs may make more power through timing, rather than airflow. Therefore, take all readings with a grain of salt.
150hp should see 120 g/s , so that's 120 divided by 0.8 = 150
180hp should see 144 g/s
225hp should see 180 g/s
250hp should see 200 g/s
You get the idea.
Another check is to test the boost pressure, pretty sure most 1.8ts stock run around 0.6-0.8bar.
Further than that you need someone who knows what they're doing with remap files to pull the software off the car and go through it to see if it's stock or 'tuned'.