Anyone here experienced said burning oily smell in the cabin? It's a 1.2tsi elegance 2011 plate, 67k.

Only comes to light when the heater is on warm and drawing in fresh air (i.e. Not in recirculating mode with A/C running) standing still (lights or in traffic)

NOT when under weigh (moving :))

Nowt when heater is set below 19 degrees, or off, or  with no fan running or on demist/AC, AC or recirculating.

No smell under bonnet or in boot (thought it might be exhaust coming in through the vents?)

Also tried sitting with the engine running, no heater or fan going and the windows down, still nothing but put the heater on and it's back!

ideas?

Firstly, make sure there is no stuff caught in the intake vents as leaves and stuff often fall into them. Also check inside the blower fan for debris. You will need to remove the pollen filter and pop your hand up in there to feel for it, with the fan OFF of course! This is just to be sure its not getting clogged and over heated as fans are expensive and require complete dash removal. You could also check any of the plastic/rubber tubing/ducting that may go from the engine compartment to the cabin as they may be holed or detached, pulling in nasty engine smells. Also, check the complete exhaust system for leaks. One old method is to run the engine and try to block the tail-pipe to see if the gases escape anywhere along the system. If it is sound, it will have quite some pressure and may force your hand/foot off the end or even make the engine stall as the gas has no escape.