My MY99 UK turbo Impreza has just failed the MOT on excessive emissions. Before i took it in it was doing the following on tickover- alternating between 850rpm and 500rpm at 2 second intervals, i.e a regularly lumpy tickover.
A friend has suggested it may be air flow meter or lamda sensor or cat gone **** up. So come on people- name that fault...

No prizes for the winner... :-)

 

Air Flow meter, these are known to be pretty damn fragile on the MY99 / MY00

 

almost certainly MAF cartridge..................carry on the shelf, they are so common to fail!!

alyn - asperformance.com

 

MAF

 

Have spoken to Power Engineering, they seem to think symptoms point to lamda sensor...

 

Almost without doubt, the MAF needs replacing ( as mentioned several times before )

 

could also be lambda.

 

When my Lambda sensor failed the revs would drop & rise when pulling up to junctions. Car ran really rich which wouldn't help emissions.

I thought a dodgy MAF would cause the car to run lean under load, not rich under closed-loop conditions ???

Stefan

 

Yep, thats exactly the situation where my idle goes a bit whacky- junctions and pulling up at the lights etc. Thanks Stefan.