Emissions high and Idle low

[benjbrooks]

Hi all,

I've had my Lupo for nearly 10 years now and in nearly every year since it has failed its emissions test with high CO. Usual procedure is to replace the cat (on warranty) and it passes. Next year rinse and repeat. This year the tester told me that the CO was high but couldn't complete the test because it "couldn't maintain its natural idle". Apparently it was idling too low. HC and Lambda is fine

My questions are why is it idling low?, how can I get it to idle faster? and why does it go through cats like hot dinners?.

Things that I've done:

• Replaced the oil breather 2 years ago (cleaned at every service since)
• Replaced the throttle body last year (calibrated on VCDS)
• Oil & Filters every year, plugs, leads and coils every other year

Car is: 2000 VW Lupo S 1.4 16v (AHW)

Thanks in advance

[Rich]

Replace the green temp sensor.

[mk2]

Yep. 

Everyone else give @Rich a plus point

 

[The Penguin]

cat cleaner in the tank and a 30 mile run before the test

[benjbrooks]

Thanks for the help everyone, replaced the temp sensor and driven about 60 miles with cataclean including a 35 min 60/70 mph run on the way to the tester but unfortunately it failed again this morning on High CO during fast idle.

The tester told me that the CO is fine for the first 10 seconds or so then rises over the limit.

Sounds to me like this cat is shot. Is there anything else that may be causing it or may destroy a new cat?

[mk2]

Are there a lot of blow by gasses from the sump? Lots of oil mist getting sucked in will increase CO levels. High CO usually means not enough air to burn all the hydrocarbons. So either too rich a fuel mix, not enough air or additional hydrocarbons from another source (like evap canister which Lupo doesn't have or oil mist gasses from the sump).

Running rich is often demanded by the ECU if it thinks the engine is cold. A rich mixture makes a cold engine run smoother. Think 'choke'... Thus the temp sensor as a good candidate for swapping.

Swapping the cat will only be a short term fix. I reckon that the cat is fine. It just needs purging (run lean for a bit). It's probably 'full'.

Edited January 4, 2024 by mk2

[benjbrooks]

There are visible fumes from the breather and always a film of oil in the air box along with an occasional lump of mayo. I assume there would be no way of fixing this without plumbing in a catch can or somehow reducing the crankcase pressure (piston rings).

Is there a way to make the engine run lean on purpose to purge the cat?

[mk2]

18 hours ago, benjbrooks said:

Is there a way to make the engine run lean on purpose to purge the cat?

I have "elephant snorkle" mods on every engine I own. Even my lawn mower. Sump gases are so bad for an engine it's crazy. Simple length of 20mm cable flex conduit from the breather outlet down towards the chassis rails under the car cures all evils. A bicycle handlebar bung works a treat to block the airbox inlet hole.

To make the car run leaner is tricky, because the ECU is monitoring the O2 sensor, checking the mix all the time while driving. Unless you make yourself a O2 emulator circuit, so you can forcibly trick the ECU to make the mix richer or leaner. Could try a small gap somehwere on the vacuum side. Perhaps even one of the vacuum lines? I guess you might be able to let some air in bit by bit (when it's warmed up), until it throws a code.