Failed MOT Emissions

[angelstar000]

Hi,
My W124 1994 just failed it's MOT on Emissions

Fast idle
CO 0.99 fail
HC 43 pass
^ 0.98 pass

Second fast idle
CO 1.10 fail
HC 45 Pass
^ 0.980 Pass

Natural idle
CO 1.15 fail

Can anyone tell me what needs to be done or what I can do to pass the retest? The garage wasn't very helpful at all!

 

[grober]

You have to look at the basics- when did you last change the air filter- when did you last clean the throat/ throttle plate of the throttle body? If dirty a sticky throttle body can effect idle. Other things to check engine coolant temperature sensor and the inlet air temperature sensor---- and the real biggie--- the MAF [ the mass airflow meter] depending on model they can be cleaned [ very carefully! ] the sensor unit replaced [Pierburg] or the entire unit changed- don't be tempted by cheap chinese knock offs they don't last get the real thing made usually by Bosch. LOTS OF POSTS ON HERE HOW TO TACKLE THIS SORT OF STUFF.

 

[ChrisEdu]

Could try talking to VW?!

 

[190]

A 94 will have a Cat ?

..and closed loop control of the injection so for me the O2 sensor looks suspect.

A CO of 1 is way high for a car with a cat even the injected engines without a cat could get below that.

 

[grober]

A 94 will have a Cat ?

..and closed loop control of the injection so for me the O2 sensor looks suspect.

A CO of 1 is way high for a car with a cat even the injected engines without a cat could get below that.

Good call and the MAF and Lambda sensor wires are often the first part of the wiring loom to get fried by the engine heat.

 

[angelstar000]

Thank you, this is most helpful.

 

[GP801]

Our 280 had a similar issue a couple of years ago. They puzzled over it for quite some time before realising both the MAF and lambda sensors were dodgy.