Gti6 emissions

[martyn92]

The car has failed on its mot for emissions, fast idle is the problem. Co is 0.6 and lambda is 1.2
It's had strong smell of fumes for a while.
I've changed the lambda sensor and doesn't seem/smell any different but it's not been back for its retest since fitting it.
It's also quite lumpy at fast idle and you can hear it quietly pop from the exhaust.

Coolant temperature sensor appears to be working okay.
Any ideas?

[PartyJas]

Have you tried an ECU reset after fitting the new Lambda sensor?

[Niall]

Change the coolant temperature sensor (green one) and take it for an Italian tune up

[martyn92]

Change the coolant temperature sensor (green one) and take it for an Italian tune up

I will go and get one tomorrow just in case. Im sure its working because of the readings from multimeter and when I unplug it, it struggles to rev/run properly.

So assuming its not the cts what else is the likely culprit? It doesn't seem down on power but doesn't seem as responsive as it used too. But not sure if thats just me because ive got used to it? (only had it a few months)

Between 2-3000 rpm you can feel the whole car shaking and hear a pop/burble every now and then

It used to idle at 500 rpm for a few seconds when starting from hot but soon went away, not familiar to gti's so assumed it was normal

[RetroPug]

When you unplug the CTS it defaults to REALLY rich fuel mixture, however it is possible that yours is failing and running a bit too rich.
You can test the CTS with a multimeter by putting the end in water of a certain temperature and reading the values.

I can post a diagram of how to test it late this afternoon/evening if that would help.

[martyn92]

I've measured it when it's been hot and the readings seem to be on par with auto data. I've not fully tested though.
I'm going to get a new one anyway but I'm just thinking of anything else that might have an effect

[martyn92]

CTS fitted and no change. Still lumpy/pop at 2-3000 rpm. Came back from a drive and still smelt strong of fumes.
Suggestions ?

[Toms306]

Lumpy at 2-3k sounds like a coil pack problem tbh. Shouldn't really cause it to overfuel though, soon as the lambda see's unburnt fuel I'd expect the ECU to reduce the amount it's chucking in... Just thinking aloud really lol, you seem to have checked the obvious things.

[martyn92]

Cleaned the throttle body too as that was quite dirty. It drives well and pulls well, however the first drive of the day it was holding the revs when off the throttle and also idled at 1100 for a second or so. First time its ever done that it and its been fine since.

All 4 plugs are like this (Engine was hot)

[martyn92]

Took it back for retest again today and failed. Passed on lambda this time but CO was still too high. 0.45%
Exhaust fumes still smell strong. New cat would probably get it through but that still wouldn't fix the rough running at 2-3000 revs. Fixing that would likely fix the emissions?

Injector/coil/sensor?

[Woody.]

Took it back for retest again today and failed. Passed on lambda this time but CO was still too high. 0.45%
Exhaust fumes still smell strong. New cat would probably get it through but that still wouldn't fix the rough running at 2-3000 revs. Fixing that would likely fix the emissions?

Injector/coil/sensor?

From past experience it's normally the cat that's given up. Is it a genuine one do you know?

Rough running could be multiple things, but seeing as you've changed lambda and CTS coils would be the next port of call I think. As a free check, if you unplug the power steering sensor does it help at idle at all?

It's down between the rad and inlet mani as is a blue plug

[powerandtorque]

Yup, I'd go with the cat having failed, probably due to the unburnt fuel from the suspect failing coil(s).

You'll usually get something in the region of 0.5% CO with a good lambda but failed cat, which is roughly what you've got.

Fit another known good cat for the MOT and I'd expect the emissions to drop right down, but unless you fix the misfire that's going to be resulting in unburnt fuel going down the exhaust you will kill the replacement cat.

Aftermarket pattern cats are rubbish btw - it'll probably get you through the MOT, but don't expect it to last.

[Niall]

As above, my money is on a dead cat due to the running lean.
Do not buy a pattern cat. Get a second hand (or if you can afford it new) genuine cat. A pattern one will just creep through the mot and I would put a pint on the fact that it won't work by the next mot.

[adam b]

Or decat and find another MOT station (cough). This will lose you a touch of low/mid range torque, but gain a little top end over the standard cat. Pattern part or 100cell jobbers are a waste of time and you will lose power and torque.

Are you happy with the idle and the way it reacts to throttle inputs, especially when you come off the throttle? The misfire thing is a bit strange..