Emmision failure at IDLE and Post CAT 02 Sensor

[nosecone]

Hi all,

The good lady has a 2.0 AQY 2000 Beetle that failed MOT with emission issues (the car not the missus) - I have VCDS and noted that the LAMBDA settings were off the scale. I kind of fixed it when I discovered most of the vacuum pipes had age related cracks. I cut off the ends and VCDS showed a large improvement in the values (in the right direction) - I had already swapped the PRE-CAT 02 Sensor and it made no difference.

Anyhow, it failed again on the re-test with highish CO2 on idle - the first and second fast idles are now OK.

My question is this - VCDS shows the POST CAT O2 sensor as not being ready. I have metered the heater at 14 Ohms but the supply voltage to it is fluctuating between 7-9Volts between pins 1-2 !!!! The PRE-CAT voltage supply is nearly 14V and stable. If I measure pin 1 to Earth it is 14V as well so I suspect it is the return to the ECU.

Looking at the wiring diagram it would seem to be an ECU issue - willing to be corrected on this.

However, the books say that the POST CAT O2 sensor has NO affect on the FUEL/AIR trim - so how likely is this issue to be the cause of the IDLE emissions problem ???

Should I look elsewhere for the emissions issue - I don't want to spend lots of time and effort on an new ECU if it isn't actually the cause of the MOT failure.

PS. No fault codes after fixing air leaks - other than today that said B1S2 sensor too slow to respond.

Thanks in advance

[zollaf]

would need to know the actual values, co and lambda. won't be the post cat lambda sensor though. more likely another air leak. when was the car last serviced, plugs, filters etc...

[nosecone]

would need to know the actual values, co and lambda. won't be the post cat lambda sensor though. more likely another air leak. when was the car last serviced, plugs, filters etc...

Hi Zollaf, thanks for the reply. Using VCDS group 32 - first figure hovers around 0 and looks okay the second figure around +15 (-10 +10 range). As I said all the indications suggest the post cat does NOT respond.

VCDS Group 1 Lambda controller now stabilizes within the +-10 range ( every vacuum hose had a cracked end on it - second question, do people replace these with genuine VAG or is there a better alternative ?)

The mot failure initially was first/second/natural test but now its just the natural idle its 0.69% with a max of 0.5%.

I dont have the actual paperwork as the garage advised me to thrash it on the motorway may clear it - so they didn't charge me - but I didn't get to keep the results.

Plugs, oil and air filter all recent.

All help gratefully received.

Paul

[zollaf]

with a figure that close i would give it a good italian test drive, maybe with some fuel treatment in the tank, then take it straight back.

[nosecone]

Still got the old pipes attached and dont trust them not to break off - so as they say on top gear going through the gates of hell on fire doesn't appeal to me !!! Will change them over ( any recommendation on brands ?) and then take it for a run ( at night its a bit girlie for me ).

[nosecone]

Took it for an MOT Re-test which it only just passed - they were very good an we tried 2-3 times to get the IDLE specs in.

I bought a vacuum gauge and it indicated 'good' around 20ins hg - I then replaced all the Vacuum hoses that were 'dodgy' and the indication went up by a couple of points 22-23 ins hg.

I then thrashed it for about 5-10 miles - but it seems to hesitate initially on hard acceleration throttle (imho).

Then I took it for its re-test and as I mentioned only scrapped through.

VCDS group 32 - when left to run for a while it seems to me the idle figure climbs upto the slightly beyond the +10 mark.

Should I still be looking for leaks if the vacuum test was okay ?

Thanks in advance

Paul

[zollaf]

any leaks in the exhaust anywhere, even tiny little ones ?