Emissions Not-Quite-Failure
 

So, MOT done for the S2K and it passed! It did apparently take 3 goes at the idle emissions test and eventually passed at a... questionably high idle RPM.

The mechanic's suggestion was one of the O2 sensors was on the way out. It's an '08 and I'm not entirely clear what part I should be looking to get. There are plenty of references to the Denso 234-4353 for AP1 in the US, from what I can see, but the AP2 apparently have a different sensor, and I don't know how that maps on to the AP1 facelift that we have in the UK? And all of them seem bloody expensive, and the Denso I referenced doesn't appear to be for sale in the UK anywhere that I've found. Any insight would be appreciated!

Normal for an S2000 !!
thought about a wideband ?
https://www.s2ki.com/forums/uk-irela.../#post23583038

ECPs and get ready for a diy kit,been there ..
feedback on your finings :tipwink:

As MB will no doubt tell you - these things are almost consumables on an S2000. Every 3 years give or take on mine and as above, it's usually the one in the CAT that goes first. Bad gas mileage is the usual sign of it.

Mine had the same issue at MOT, I could hear them revving pretty hard to get it to pass - good to know what to shop for next
I normally go to Rockauto.co.uk and put in 2003 to get engine parts for the AP1 with F20C but in this case it does look like there was a change in sensor for the UK F20C Drive by Wire years from 36531-PCX-014 (1999-2005) to 36531-PZX-013 (2006-On)

According to Lings (assuming I have the right part!), the MY09 part number is 36532PZX004

https://www.lingshondaparts.com/hond...2&block_05=hcr

This is the DENSO 2344353 {#36532PZX004}

Hope that helps?

So, if it's the one in the cat the "rear" sensor that's dead / dying there's the lovegroova-posited DENSO 2344353, Honda Part# 36532PZX004 for £260
As far as I can see the Bosch £77 at ECP that Nottm_S2 mentioned is also downstream

The "front" sensor is the wideband one (?) like this £270 one at ECP, or the item marked #7 on the diagram here, Honda Part# PFKL539926 marked SENSOR, FUEL AIR RATIO for £260, although h-tune seems to have them at £193 atm

I'll look to pick up the Bosch £77 one and report back. Might take a little longer than I'd like because I'm moving house at the moment.

Thanks for the all pointers!

The downstream sensor that sits in the cat will not affect how the car is running, so unless you got a CEL for that sensor there is no need to change it.

No CEL, which means the more expensive upstream one then! Thank you :)