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[swordfish]

looking for ideas ,, 2.6 v6 failed mot on  emissions at fast tick over ,, one thing i have noticed is there does not seem to be  cold start working from cold and it has a very slight rough tick over . 

[dave the builder]

do you have a print out of the readings ?

[Bigron]

I have found that a dose of Cataclean, a tankful of Shell V-|Power and a damn good thrashing  (NOT Basil Fawlty style!) reduces the emissions to sub-MOT level. 

Ron.

[Kevin Wood]

If it's already not running well, then it points to a fault, IMHO.

Is the EML on? Are there any codes stored?

[swordfish]

co mot fail
fast idle test fail 2.250%
second fast idle test fail 5.828%
natural idle test fail 6.478%

no warning lights on

[Nick W]

Check all the intake pipes and hoses for leaks.
But do it as part of fitting a new thermostat.

[dave the builder]

If the wet stat is stuck open, as Nick W says ,the ecu will fuel for cold start .
If you can get live data that helps ,cheap obd2 scanner /torque app ,that naughty scanner  or similar
see what the ecu coolant temp sensor is showing .
vauxhalls over fuel when cold (or the ecu thinks it's cold )
a duff cts coolant temp sensor can read -40 degrees 
you will also be able to see stuff like lambdas switching and all that good stuff
cataclean I have used many times , I tend to put cataclean in a week or so BEFORE mot in 1/4 of a tank of fuel, use it till the light comes on , then , fill with fresh petrol.

getting the cat nice and hot BEFORE emissions test helps alot 

check exhaust for blows (even small ones) check breathers and air intakes for leaks /blockages

[swordfish]

just thought i would add the car will not reach full revs under load it starts to misfire

[Kevin Wood]

co mot fail
fast idle test fail 2.250%
second fast idle test fail 5.828%
natural idle test fail 6.478%

no warning lights on

That's running very rich. 

As said, need to check live data, to see if the ECU temperature sensor is reading OK and, if so, check the other inputs to the ECU.

[swordfish]

were is the thermostat temp sensor .
thankyou

[Doctor Gollum]

were is the thermostat temp sensor .
thankyou

Thermostat is it's own temperature sensor

ECU one is next to the dash one on the coolant bridge... Plug is identical to the purge valve (on back of 135 head) but voltages are different... Ecu one is 5v, purge valve is 12v, but both plugs reach both items...

ECU temp will be showing as - 40 on diagnostic gubbins

[swordfish]

so that's the one with 2 wires going in to it blue plug .
thankyou

[swordfish]

Hi,, just come across a round black sphere about 2" long nr the temp sender with a 2 wire plug  . one blue and one grey and what looks like a vacuum nipple. but its not connected to anything and there is no vacuum pipe connected . any body no if and what it should be connected to .
thankyou

[Doctor Gollum]

That's the purge valve

One pipe goes to breather bridge, tother to the tank behind the driver's wheel arch.

If it wasn't connected to the breather bridge I am not surprised it won't idle right

[swordfish]

its broken off at the bracket end ,, but problem is there is no pipework