Back story: I bought another S40 because it was a white, manual T4 and it was cheap. I knew it had a bit of a pong to it, but assumed it was mostly the owner sitting next to me.
Nope...
I later discovered that the back of the ashtray had been cut out (presumably to let a phone charger pass through), and then some champion had used it anyhow... Now the whole area in front of the console was an ashtray...
Decided that I had to do this properly, I ripped the interior out.
The floor and any plastic parts were scrubbed with truck wash.
The carpets were scrubbed and hosed and scrubbed and hosed. Amazing how much foul looking gunk came out.
Rear seat was swapped with another one I had. Unfortunately the matching front seats are the earlier type and have the different airbag sensors, so I had to put the originals back in.
Everything else was wiped over with a vinegar & water mix. And I mean everything. Many hours of fun, discovering bits and surfaces that I never realised existed.
And now the smell is much better, but not perfect. When you first get into the car, you can notice it, but it goes away quickly.
I have a couple of trays of bicarbonate soda sitting on the floor.
Will do the vinegar wipe again.
Any further suggestions before I just try to mask the smell with air fresheners?