Limp mode is when the ECU senses that it is getting an invalid input or problem and to protect the engine from being damaged it reduces power usually by restricting ignition advance and richening the mixture.

Often disconnecting the offending sensor will cause the ECU to ignore the sensor and revert to another map, usually this will restore some of the performance.

1.8Ts are famous for having failing MAFs, unplugging them makes them run much better.

If you have a timing light, hook it up and rev the engine while monitoring the timing. The timing should be pretty stable at tickover and then disappear out of sight as the revs increase. I would expect the timing to exceed 25 degrees easily above 3000 revs.

I am pretty sure that the KR 16V for example doesn't advance the timing with the vac pipe off. Therefore the engine is stuck with the base timing of 6-8 degrees which is no where near what it needs to make any power.

Gavin