Renault megane cutting out?

My 2003 Megane 1.6vvt starts and runs fine, however when i get stuck in a bit of traffic the temerature sensor drops suddenly to cold and the car idles irratically and sometimes stalls. When it stalls i cannot restart it, has anyone had a similar problem and know what it could be / how to fix it.

The error code says a problem with the dephaser pulley, but it starts fine with no knocking and sounds good on startup so i'm not sure if this is the case.


thanks alot