Your fellow motorist was probably correct, as suggestions here, the renault forum is the best place to get your answer.
I am a moderater on the Renault Forum, it is well worth joining if you have any Renault,
This thread on the forum will show you how to fix it..............
http://www.renaultfor...ght=megane+tdc+sensor
Renault call the crankshaft sensor "the TDC"
You could fix it without spending a penny, follow the instructions but 90% of the time all you need to do is clean the Sensor, after a few years the sensor pick up gets dirty and starts playing up, all it needs is cleaning, also make sure the connecter is clean.