Didn't really cause a flat spot, the car kept pulling ok upto redline but after 5500rpm it pulsed on/off. 32008AA091 is the part number for the sensor I bought. £35 from ebay free p+p. http://www.fbtuning.co.uk/phantom-misfire-fault-codes/ if you follow this link and scroll down, there is a data log graph of the nps doing exactly what mine did. I would recommend removing the pitch mount under the intercooler to change the sensor as its right on top of the box, still not easy to get to. Took me 1 1/2 hours still!