Is the car shipped at all? Usually, what is ment by overboosting, is that the boost exceeds the allowed maximum value programmed in to the chip in the ESC-II unit. In a standard car this limit would be at around 0.7 bar. If the limit is exceeded for more than 1-2 seconds the ignition is cut completely, which results in a very abrupt loss of all the power. Also the tach would drop to zero. Is this the case?
If it's just blowing out the spark, the loss of power would be very different, as in the car coughing and hesitating.
If you wan't to install a lambda, you need to weld a boss for it to the down-pipe.