Porsche Enthusiasts Club Forum

Each year the ol '44 struggles to get through the MOT on emissions. I am fortunate that the place I take it wants to see it pass, and so always spends a bit of time getting it up to temp, or fiddling with the only control available - the AFM screw. It has been successful again this year, the car was taken for a good 'blast' down the road and then back on the analyser to record a good result. However, I am not happy to leave it at that and want to try and get to the bottom of the higher than normal CO2 readings (the HC is fine). So, I will shortly strip the intake assembly and clean the bypass valve, the throttle body, etc. Check for vac leaks, look at the AFM track and give the AFM a bit of a service. In fact, I have a complete intake assembly from my donor car that I could service, clean and simply fit..that might be easier?

I have noticed that the idle speed does seem to always be a little higher than I would have expected (around 1100, where it should be 800-900), so something is amiss. Generally, the plugs look good, so is there anything else in addition to the above that I should be on the lookout for?

Also, has anyone had experience of the Gunson G4125 Gastester? It looks like it might be able to help while I 'play' and investigate the issue, what do you think???

Generally high CO is AFM or TPS. Been done to death on here so worth a search.
The Gunsons GasTesters work well I have one & they are great for MOT test go/no-go type tests. Generally most 944s will be around 1-1.6%
Worth a look for airleaks as well, that could be your high tickover.

Try having it Terracleaned if everything else us ok ! It does everything from Injectors, top end through to exhaust. I had mine done,it cost me £90. (150,000s2) . Made a noticeable difference to the way the car pulled and got a much better idle ( passed mot with ease) ! If you have a look around on Google there are plenty of cases of mot fails ,being passed after being cleaned!

I had the same problem for about 5 years, used to end up taking her for a 10 mile spirited drive before taking her in for the MOT to try and help, a replacement AFM from Promax sorted the problem.

My s2 recently failed on emissions and then passed easily after the AFM was cleaned and recalibrated by my local indie.