I have 2004 mk1 Skoda Octavia 1.4 petrol. 
It is fine driving but won't hold revs above around 1700 when idle. This only happens when the engine is hot. This prevents it being tested for emmissions and has failed the test. 
The car has had new:
Crank sensor 
Cam sensor
Upstream lambda sensor 
Downstream lambda sensor
Knock sensor 
PCV valve
EGR & throttle gaskets
Spark plugs
Fuel filter 
Air filter
Oil filter 
Oil
Second hand:
Fuel rail and injectors
EGR valve 
Throttle .

Injectors EGR valve and throttle have been cleaned. 
Throttle position has been reset. 
No codes. 

Anyone got any idea how to sort this out? Any help would be much appreciated. 
 

Your car is a bit early but might have the same ECU programming that mine and all other later vehicles have, in my case the engine will not rev above 2.5k rpm when at standstill, the wheels have to be turning even very slowly for it to rev any higher.

 

Try rolling the car forward in first gear, declutching while it is still moving and revving the engine, I bet it will then rev.

 

It should not "fail" the MOT test, it should be passed with a note that the emissions could not be checked as the engine could not reach the RPM stipulated in the procedure, thats what happened to mine, the tester is a good friend and he explained exactly the whys whats and wherefore of my pass certificate.

More nonsense from @J.R.!  The OP is in Ireland, so has to follow NCT rules , not UK MoT rules or French Control Technique rules.

Thankyou once again Ken for your kind comments.

 

I am partially sighted and can only read with the macular vision of one eye, an icon can be flashing elsewhere on the screen and I will not see it, I had not seen the OP's location, thankyou for pointing it out in such a discreet fashion.

 

I made no mention of France or the CT test.

 

Setting aside your pleasure at throwing insults around the problem of emissions testing a vehicle like mine and all EU5 model VAG vehicles that can not rev above a low threshold at standstill will necessitate a solution in any country, soon I will find out how the French deal with it, a FWD vehicle could be tested on the brake rollers but not a 4WD one like mine.

 

Perhaps they are or will be able to connect to the OBII socket and disable the feature while testing, there was talk of downloading of fault codes being part of the test.

Edited 5 December, 20214 yr by J.R.

11 hours ago, J.R. said:

Your car is a bit early but might have the same ECU programming that mine and all other later vehicles have, in my case the engine will not rev above 2.5k rpm when at standstill, the wheels have to be turning even very slowly for it to rev any higher.

 

Try rolling the car forward in first gear, declutching while it is still moving and revving the engine, I bet it will then rev.

 

It should not "fail" the MOT test, it should be passed with a note that the emissions could not be checked as the engine could not reach the RPM stipulated in the procedure, thats what happened to mine, the tester is a good friend and he explained exactly the whys whats and wherefore of my pass certificate.

But the car is fine when the engine is cold. 

Indeed, I dont have a suggestion which could explain explain that anomoly but thats often the case, from what you have said it will not rev (when cold) at standstill (I think you said from idle) but it drives fine so it is well worth doing my test perhaps at varying engine temperatures and then working from hopefully more information to find a solution or cure.

Is it the revs at 2,500 rpm for 20 seconds that it can not hold?  Is that what you mean as 'idle above 1,700?

https://ncts.ie/media/wiwmmcpc/nct-manual-june-2021.pdf

 

 

Edited 5 December, 20214 yr by roottoot