Smell in cockpit of S3 OTS

[Heuer]

The biggest culprit is the interface between the fresh air volute (bit with the fan in) and the rubber seal on the air intake. This is usually caused by the (reproduction) heater/volute assembly not being aligned properly during manufacture. The heater box is usually perfectly level as it is bolted to the bulkhead but the volute can dip down meaning the seal does not engage properly when the bonnet is closed. Place a steel ruler on the heater box and check the level of the volute

Easy to test further using talcum powder. Dust it evenly on the rubber seal, lock down the bonnet on on opening check the talc witness marks left on the volute. There should be a perfect circle, if not you have a leak allowing vapours to enter the system. About the only fix is to add spacers to the bottom mounts of the box as it is impossible to bend/rework the assembly. It does mean the heater box itself is tilted slightly upwards although it is not really noticeable, You will need fairly large spacers (maybe 1/2") for the bottom mounts as you need to raise the front of the volute some distance away.

[Rui]

Quite a late answer , but I had this problem on my S3 OTS, mainly when driving top up and driver window slightly open.

The major issue is turbulence of airflow and exhaust coming back in the cockpit.
S3 also usually leaks oil from the valve covers to the exhaust manifolds, originating nasty fumes.

I have a much better situation now:

1 ' Make sure the exhaust connections under the car are tight
2 - check the rubber cap on the top right side of the engine, used for chain tensioning , It gets brittle, it is usually a major cause of oil leak and it not air tight it does not allow a lower pressure inside the crankcase so fumes will escape instead being absorbed by the recirculation system. This is important
3- Another major improvement had to do with tuning carbs so that you will get CO around 3%. Due to a wrong fuel needle valve the right carbs, i had 8% and for years. I could not get it down until i, when rebuilding the RH carbs I noticed that the fuel needle valves on the RH carbs were 2.5 and not 2.0 as they should, allowing a too rich mixture.

2 and 3 made a big difference , as well as making sure there were no oil leaking from the valve covers to the exhaust manifolds.

Rui

[lowact]

So - if somebody does have an answer - pls put me out my misery...

Sorry Tim no answer, only questions:
Did you try blocking the openings that connect the boot to the rear of the cockpit? Did you try temporarily sealing the boot by taping over the boot lid gap?
My theory is that if we can stop the boot overwhelmingly capturing exhaust fumes and channelling these into the cabin, then some of the other measures you have tried may be more effective ?

[lowact]

Another thing to try: Driving with the boot unlatched, the slipstream holds the boot lid partially open. Supporting and fixing the lid in this positon, what does that do to yr wool?
Have you tried wool on any other car , is it any different?