2001 Octavia MOT emission test wont stay at 2000-3000 rpm

[jw71]

Hi

 

I'm looking for some help on my 2001 Octavia its a 1.6 petrol engine code AVU we have it for 8 years it done just over 160,000 mile and still runs really well however I have had a problem getting it through the MOT as the test station can't test the emissions as the rpm wont stay between 2000 and 3000 rpm.

 

The car will idle between 2000 and 3000rpm when its cold but as soon as it gets warm the rpm either:

•  just drop out to 1000rpm if you make the slighted adjustment on the pedal
• or keeps going up to 4000rpm if you keep it in the same position

I have cleaned the throttle body and checked for air leaks but can't seem to find anything, I have also had a garage run diagnostics and check it over and the fault code was the lambda sensor which has been replaced. Since then I have re-run diagnostic and had another emission test this resulted in no other faults beign highlighted and the car passing the emission test albeit at 4000 rpm.

 

The problem is the MOT station tell me that they are unable to give me a certificate as the the car wont idle between 2000 to 3000 rpm, I have taken it to another test station and they have said the same.

 

If you have any idea how I can fix this that would be great?

 

Thanks in advance          

[fordfan]

I don't usually bother to measure the engine speed when I test them, for this reason.  However if the testing station feel that they do, I've had some success in the past by loading the engine.  This can be done by having all the electrics on, air conditioning on and the steering on full lock.  Unfortunately this is at odds with the testing manual procedure, so it may be the case of having to compromise on this part of the test.

[pauldazzle]

If you have a black coolant temp sensor fitted, change it for a genuine VAG revised green CTS. It's a very common failure & will cause incorrect fuelling which can cause emissions problems. N.B. You can't rely on fault codes with the CTS as if it is still outputting a signal, even if it's wrong it doesn't cause the ECU to throw a code.

[TeflonTom]

It could be the pedal position sensor failed, or the throttle body is worn.

[germen]

In my case I should put on the air conditioned and it worked.

Regards from Spain.

Edited 22 October, 2014 by germen

[jw71]

Thanks for your responses

 

From a cost point of view I have tried loading the system/air con etc but this didn't work, I have also replaced the temperature coolant sensor but again this didn't make any difference as the engine will not hold between 2000 to 3000 rpm when it’s warm, which means the test station won’t pass it even though it passes the emissions at 4000rpm.

 

I am going to try and source a throttle body but it will have to be a used part as its really not worth buying a new one

 

Any other cost effective suggestions would be gratefully accepted