EMISSIONS PROBLEM, MOT FAILURE, E230

Any help with this would be greatly appreciated!
1996 E230 Estate (Model 210), failed MOT test because the emissions (CO2) are too high. It has had a new catalyst fitted 2 months ago, a
new temperature sensor, so far no change to the problem. I'm about to change the <excuse spelling> "Lamda" (Oxygen sensor in the exhaust manifold).
I've had it checked on a Mercedes diagnostic computer and the results have so far been inconclusive.
Any suggestions as to how to reduce these emissions? It's currently reading CO2 0.4 and I believe should be below CO2 0.33.
Thanks in advance,
Chris
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Chris Wood wrote:

CO2 ??? As in Carbon Dioxide ?
Or CO, as in Carbon Monoxide ?
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Chris Wood wrote:

You don't state when this motor was last tuned up - new spark plugs etc. or the total miles on this engine - if over 150K miles the engine's compression may be low. Another thought is dirty fuel injectors, which can be removed and professionally cleaned for about US$20/ injector - such injector service is also available in the UK.
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FWIW, as you know, CO2 emissions are the basis for vehicle excise duty in the UK, however mad that might be.
Does the garage that did the MOT test not have a comment? My old 190E 2 l (1993) hasn't failed on emission grounds so far...
DAS
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For direct contact replace nospam with schmetterling
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