'95 P38a 4.6 (No LPG fitted)
The Beast just failed with readings of:

Fast Idle: CO = 0.405 (needs to be max. 0.300)
Second Fast Idle: CO = 0.405 (needs to be max. 0.300)

Lambdas OK
HC OK

Testing garage says: new cats.
Second opinion garage says: Lambdas (as if cats are u/s it would have failed HC)

Have put best Shell petrol in. Bottle of Cataclean (slight improvement)

Would it be worth fitting a new air filter (or removing it for the re-test)?
Worth cleaning the MAF?

Any further suggestions would be gratefully received!

Air filter change might affect consumption but not emissions to any degree.

I'd say if you've given it a good hard run to flush the cat's and it still is wrong then while the cat's affect to a degree what you get out of the exhaust pipe, they are a passive device, while Lambda's are active devices with a lot of control over the fuel trim at most stages of the throttle opening.

I'd go for the Lambdas, but get some live readings to see if they are toggling up and down as they should do.

Peter

Peter

Many thanks for your response. I find the MOT to be more stressful than moving house. In my view Cataclean is over-rated, there was a very slight improvement in CO but in my case, not worth the money. But then again if the Lambdas are knackered I can't blame Cataclean.

I now have the least expensive answer; new MOT for £30 and the garage are going to stick the probe up another car's tailpipe..............

I've never used an injector/cat cleaner, best not get involved. If you need anything more after a good road run, then better to fix the problem rather than get a temporary or marginal improvement with 'sticking plaster remedies'.

Peter