This stunning car arrived last September. Now ever since I got it the tickover has always been around 800/900 rpm in or out of gear. Just of late it's got a mind of its own, sometimes it will drop to around 600/700rpm, still nice and smooth. Other times it will start at the 800rpm and then after a short drive, stop at a junction and it will suddenly drop to 600/700. Just wondering if I have. Sensor on its way out, could a man sensor cause this. Any ideas?