MOT fail over-revving failed exhaust emissions
Discussion
Hi Everyone,
I hope someone can give me some peace of mind.
My car failed its MOT today. It failed because it is revving when idle and they said that therefore it failed all 3 exhaust emission tests.
I'm afraid I do not understand cars very well, but my car has been over-revving for some years, so I have looked into it. One garage did try to fix it but whatever they did, did not work. Apparently it is a common problem with Zafiras and often it can cost a large amount of money to fix, because garages keep trying things that don't work.
Anyhow, with a 10 year old car and little money to throw around, I have not worried about it. It's annoying but the car seems to work ok.
It has never failed an MOT because of it.
Would you expect it to have failed because it is over-revving?
The garage was recommended to me and they seem really nice, but unsure because it has not happened before and not sure why they asked to keep the failure notice.
I am going to get it fixed tomorrow via an electrical place they recommended and then go back for a re-test.
I have changed garage, because I got ripped off at the last one and so I am nervous about it happening again.
Does this failure sound right?
Many thanks in advance.
Missie
I hope someone can give me some peace of mind.
My car failed its MOT today. It failed because it is revving when idle and they said that therefore it failed all 3 exhaust emission tests.
I'm afraid I do not understand cars very well, but my car has been over-revving for some years, so I have looked into it. One garage did try to fix it but whatever they did, did not work. Apparently it is a common problem with Zafiras and often it can cost a large amount of money to fix, because garages keep trying things that don't work.
Anyhow, with a 10 year old car and little money to throw around, I have not worried about it. It's annoying but the car seems to work ok.
It has never failed an MOT because of it.
Would you expect it to have failed because it is over-revving?
The garage was recommended to me and they seem really nice, but unsure because it has not happened before and not sure why they asked to keep the failure notice.
I am going to get it fixed tomorrow via an electrical place they recommended and then go back for a re-test.
I have changed garage, because I got ripped off at the last one and so I am nervous about it happening again.
Does this failure sound right?
Many thanks in advance.
Missie
could be any number of things. Not familiar with the zafira but something like a sticking idle control valve would be the prime suspect. Or an air leak somewhere.
First step should be letting someone with a code reader have a talk to the ECU to see what fault codes the computer is showing, might make it obvious and therefore easy to fix.
Where are you based, might be someone on here can recommend a good garage for you.
First step should be letting someone with a code reader have a talk to the ECU to see what fault codes the computer is showing, might make it obvious and therefore easy to fix.
Where are you based, might be someone on here can recommend a good garage for you.
Edited by bigdods on Thursday 28th October 21:53
I believe that an abnormally high idle speed is a valid reason for failure. See here:
http://www.motuk.co.uk/manual_730.htm
http://www.motuk.co.uk/manual_730.htm
Thank you bigdods and RB5.
It was code checked and came back too rich (I think) but said could be a number of things causing that and would have to come in to be checked.
It does all sound reasonable, just don't understand why hasn't failed for this before.
It does however sound like they are doing the right thing and it would be good if it was something like an idle control valve, as that does not sound too expensive or difficult?
I did read up something about too much speed when idle, but the thing I read was in reference to the car's normal speed and I have no idea what that should be? I'll definitely read your link.
Thanks again for responding - feel much more confident leaving my car in their hands tomorrow.
Best Wishes
Missie
It was code checked and came back too rich (I think) but said could be a number of things causing that and would have to come in to be checked.
It does all sound reasonable, just don't understand why hasn't failed for this before.
It does however sound like they are doing the right thing and it would be good if it was something like an idle control valve, as that does not sound too expensive or difficult?
I did read up something about too much speed when idle, but the thing I read was in reference to the car's normal speed and I have no idea what that should be? I'll definitely read your link.
Thanks again for responding - feel much more confident leaving my car in their hands tomorrow.
Best Wishes
Missie
One thing to note is that, contrary to what a lot of people on here might think, the garage have not failed it so that they can do the work themselves - they've told you to go elsewhere. Doesn't sound like they're ripping you off. Thumbs up from me.
ETA - normal idle speed is approx. 750rpm.
ETA - normal idle speed is approx. 750rpm.
Edited by Fane on Thursday 28th October 22:22
Could be the idle control valve if the revs are seeking and not settling down to a normal idle, or as mentioned above an air / vacuum leak.
It is possible to clean an idle control valve, plenty of guides on Google on how to do this and is generally no more than a few screws to remove the part and seperate it for cleaning. It's a simple enough job to do yourself and can atleast rule it out as being a culprit.
New idle control valves cost around £25-40 for a Zafira depending on engine model and where you source parts from, it is a 10 minute job for a garage to swap.
It is possible to clean an idle control valve, plenty of guides on Google on how to do this and is generally no more than a few screws to remove the part and seperate it for cleaning. It's a simple enough job to do yourself and can atleast rule it out as being a culprit.
New idle control valves cost around £25-40 for a Zafira depending on engine model and where you source parts from, it is a 10 minute job for a garage to swap.
My Saxo failed on this, as it was explained to me its not that it failed the test but due to the higher revs he couldn't get an accurate reading from idle to actually perform the test.
I took the idle air control valve off and gave it a clean, that seemed to have sorted the problem for long enough to get it through the MOT.
I took the idle air control valve off and gave it a clean, that seemed to have sorted the problem for long enough to get it through the MOT.
Missie said:
I did read up something about too much speed when idle, but the thing I read was in reference to the car's normal speed and I have no idea what that should be?
That's right according to the link:Reason for rejection:
A. All vehicles
1. The engine
a. is idling at a speed clearly above its normal idling speed
b. emits dense blue or clearly visible black smoke for a continuous period of 5 seconds at idle
c. emits excessive dense blue or clearly visible black smoke during acceleration which would obscure the view of other road users.
I suppose this could explain how it passed until now, since there's no definitive figures that they're looking for. Out of interest, what sort of speeds does it currently idle at?
Edited by RB5 on Thursday 28th October 22:39
I test for a living, if the idle speed is out of range the machine will fail if I am afraid.
Ours uses a sensor we place on the engine and it picks up the vibrations to work out rpm, it is very accurate believe it or not, the specs programmed into the test equipment are pretty wide, it is someting like 500-1500 rpm, outside this range it cannot take a reading, this is because at cruise, i.e. over 1500 rpm or so the engine will lean out anyway and the test wants to see a natural idle reading.
To be honest, this is the part of the test I hate, I work hard to give the car every chance to pass gas testing and sometimes you finally get it through and the bloody machine won't print the result and you have to do it all again...
Edit for too much wine consumption, any further mistakes, bite me !
Ours uses a sensor we place on the engine and it picks up the vibrations to work out rpm, it is very accurate believe it or not, the specs programmed into the test equipment are pretty wide, it is someting like 500-1500 rpm, outside this range it cannot take a reading, this is because at cruise, i.e. over 1500 rpm or so the engine will lean out anyway and the test wants to see a natural idle reading.
To be honest, this is the part of the test I hate, I work hard to give the car every chance to pass gas testing and sometimes you finally get it through and the bloody machine won't print the result and you have to do it all again...
Edit for too much wine consumption, any further mistakes, bite me !
Edited by Athlon on Thursday 28th October 22:38
Thank you very much guys for all your advice!
Not been able to get back on the site for a little while - no doubt my computer is playing up now.
I have written it all down, so I can try to understand anything they say tomorrow. I'm afraid I would not know where to even find a valve, let alone clean it, but I'd hope the other garages previously would have tried that and it has never been fixed.
My major concern was that I wasn't paying out unnecessarily and it sounds like it is totally logical that it failed.
I am probably going to give the wrong reading but it revs from 0.5 to 1.5 and hardly ever go backs to zero. Sometimes (and most embarrassingly) it really revs at the traffic lights, like I am trying to race someone i.e. like I keep pressing down the accelerator.
Thank you again Mr Pickle, Fane, Stevo Cally, The Cheesmam, RB5, bigdods and Athlon - it's good to know that although it's going to cost me, I might have found a good garage I can trust and that is great - thank you.
Not been able to get back on the site for a little while - no doubt my computer is playing up now.
I have written it all down, so I can try to understand anything they say tomorrow. I'm afraid I would not know where to even find a valve, let alone clean it, but I'd hope the other garages previously would have tried that and it has never been fixed.
My major concern was that I wasn't paying out unnecessarily and it sounds like it is totally logical that it failed.
I am probably going to give the wrong reading but it revs from 0.5 to 1.5 and hardly ever go backs to zero. Sometimes (and most embarrassingly) it really revs at the traffic lights, like I am trying to race someone i.e. like I keep pressing down the accelerator.
Thank you again Mr Pickle, Fane, Stevo Cally, The Cheesmam, RB5, bigdods and Athlon - it's good to know that although it's going to cost me, I might have found a good garage I can trust and that is great - thank you.
MrPickle said:
Sounds like it could be either the Idle Control Valve, Or the MAF (Mass Air Flow)sensor.
Both are a fairly simple fix and not too pricy.
You should be able to eliminate the MAF just by unplugging it. The ECU should go into a default/limp mode and the revs at idle will settle down straight away. Both are a fairly simple fix and not too pricy.
If its running rich it will be hitting your fuel consumption hard. Could be a lambda sensor out of whack too. It may be tricky to track down, but I would have expected a bit more from the ECU in the way of codes to be honest. Maybe ask them to check it again.
Do you ever have problems starting it or does it ever stall ? Not unusual for vauxhalls to behave in mysterious ways when the crank sensor fails but that should throw a code in the computer.
Did a quick search around a few forums. MAF came up quite a few times, as did EGR valve. One person also had similar symptoms with a failing coolant temp sensor.
Luckily the MAF, Temp Sensor, ICV and EGR are all fairly easily and cheaply checked so lets hope its one of those.
I hadnt thought of the temp sensor but if its running rich then this could mean the ECU is getting a low reading from the sensor so effectively running a rich mixture to compensate. If the place you are going to has a Tech2 or similar (vaux diagnostic code reader) it can show live data so they should be able to see the temp sensor readings without messing around too much.
There were also a few mentions of a blocked inlet pipe - not sure what they meant by this, I assume they are talking about the breather pipe(s) maybe mention to your garage as a possible, it shouldnt take long to clean out the breathers.
ETA: Also found one guy who'd had a cracked exhaust manifold - this introduces air into the exhaust gases making the lambda sensor in the exhaust think the engine is running lean (too much air in the exhaust) so the ECU adds fuel making the mixture rich, then cycles it back to lean causing revs to move around. Would also expect this to be accompanied by a loss of power.
As you can see , this isnt a simple one to diagnose !
Luckily the MAF, Temp Sensor, ICV and EGR are all fairly easily and cheaply checked so lets hope its one of those.
I hadnt thought of the temp sensor but if its running rich then this could mean the ECU is getting a low reading from the sensor so effectively running a rich mixture to compensate. If the place you are going to has a Tech2 or similar (vaux diagnostic code reader) it can show live data so they should be able to see the temp sensor readings without messing around too much.
There were also a few mentions of a blocked inlet pipe - not sure what they meant by this, I assume they are talking about the breather pipe(s) maybe mention to your garage as a possible, it shouldnt take long to clean out the breathers.
ETA: Also found one guy who'd had a cracked exhaust manifold - this introduces air into the exhaust gases making the lambda sensor in the exhaust think the engine is running lean (too much air in the exhaust) so the ECU adds fuel making the mixture rich, then cycles it back to lean causing revs to move around. Would also expect this to be accompanied by a loss of power.
As you can see , this isnt a simple one to diagnose !
Edited by bigdods on Friday 29th October 00:40
Thank you bigdods and sleeble.
I think the plan is to hook it up to something while they test the various things it could be. They do have the same code reader as Vauxhall.
It does sometimes stall just after I start it and then it takes longer than normal to start it again.
It would be great to think it is using more fuel than it needs to, as I do a lot of miles and as I am sure you'll agree, fuel is SO expensive now. So if they fix the problem and it uses less that would be great.
Thank you bigdods for looking into it for me - that is exactly why I have not pursued it before, because it sounded like an expensive investigation with many people saying the fault had never been fixed. Hopeful it will be now and I will get through the MOT.
Spleeble, it has actually been a really reliable car up to now, expecially considering the mileage (165,000). I've had it from new, but if I won the lottery tomorrow, it would not be top of my list for a new car!
Thanks again; really apprecaite it.
Missie
I think the plan is to hook it up to something while they test the various things it could be. They do have the same code reader as Vauxhall.
It does sometimes stall just after I start it and then it takes longer than normal to start it again.
It would be great to think it is using more fuel than it needs to, as I do a lot of miles and as I am sure you'll agree, fuel is SO expensive now. So if they fix the problem and it uses less that would be great.
Thank you bigdods for looking into it for me - that is exactly why I have not pursued it before, because it sounded like an expensive investigation with many people saying the fault had never been fixed. Hopeful it will be now and I will get through the MOT.
Spleeble, it has actually been a really reliable car up to now, expecially considering the mileage (165,000). I've had it from new, but if I won the lottery tomorrow, it would not be top of my list for a new car!
Thanks again; really apprecaite it.
Missie
Could also be the coolant temp sensor - if it thinks the engine is cold, then the ECU will keep the car in the warmup program (like driving about with the choke out on an older car). That'll make the idle speed high (1200-1800rpm depending on the exact engine and how cold it thinks it is), and also make the engine run rich.
Dear HellDiver,
Your post really made a huge amount of sense, because long ago when I first started driving and knew even less about cars than I do now (!) I remember trying to start each time with the choke out because that was what I had been told to do - they did not mention not every time! However, the way my current car has been behaving has reminded me of that time.
So I have just rang the garage to ask them to check what you suggested, but apparently they have already found the problem - the throttle body; it was all clogged up with no air around it?
Does not mean too much to me apart from the logic that revving and throttle are connected and it has already been said that too much air equals too rich a mixture?
So thank you very much for your suggestion, because it made a lot of sense; don't know if the two are connnected.
Many thanks
Missie
Your post really made a huge amount of sense, because long ago when I first started driving and knew even less about cars than I do now (!) I remember trying to start each time with the choke out because that was what I had been told to do - they did not mention not every time! However, the way my current car has been behaving has reminded me of that time.
So I have just rang the garage to ask them to check what you suggested, but apparently they have already found the problem - the throttle body; it was all clogged up with no air around it?
Does not mean too much to me apart from the logic that revving and throttle are connected and it has already been said that too much air equals too rich a mixture?
So thank you very much for your suggestion, because it made a lot of sense; don't know if the two are connnected.
Many thanks
Missie
Mucky throttle body then, aye that sounds familiar!
I cleaned mine out a few months ago. An easy job, just whip off all the air intake tubes and liberally spray with carb cleaner. You can be more thorough and take the off the throttle body itself, but try it with in situ first - both with the engine running and turned off.
Make sure they do the vacuum tube that connects to the top of the cylinder head too - quite surprising the amount of 'clag' that builds up in it!!!!
I cleaned mine out a few months ago. An easy job, just whip off all the air intake tubes and liberally spray with carb cleaner. You can be more thorough and take the off the throttle body itself, but try it with in situ first - both with the engine running and turned off.
Make sure they do the vacuum tube that connects to the top of the cylinder head too - quite surprising the amount of 'clag' that builds up in it!!!!
Hi Fastra,
What I don't understand is why nobody did this before? It's been a long standing problem and it is serviced regularly. I fully admit that I don't have a clue, but logically if it is so easy, why would they have not tried this when it started over-revving?
In my next life I must go on a basic car maintenance course; I do the oil, water, air in tyres etc, but I would not know where to start with anything else.
Anyway on a positive note it is fixed, it has passed its MOT and tomorrow I can catch two buses to get it back.
Thanks very much for your post.
Missie.
What I don't understand is why nobody did this before? It's been a long standing problem and it is serviced regularly. I fully admit that I don't have a clue, but logically if it is so easy, why would they have not tried this when it started over-revving?
In my next life I must go on a basic car maintenance course; I do the oil, water, air in tyres etc, but I would not know where to start with anything else.
Anyway on a positive note it is fixed, it has passed its MOT and tomorrow I can catch two buses to get it back.
Thanks very much for your post.
Missie.
Don't know really. 
Its only through forums that I stumbled across this solution really (http://www.astraownersclub.com), when trying to sort out a hesitation problem on my Astra (quite possibly the same engine as yours) which then turned out to be the dreaded EGR valve.
I suppose a garage may just try the part replacement route first as that's what they can make most money on?? I don't know - I'm guessing.
Its only through forums that I stumbled across this solution really (http://www.astraownersclub.com), when trying to sort out a hesitation problem on my Astra (quite possibly the same engine as yours) which then turned out to be the dreaded EGR valve.
I suppose a garage may just try the part replacement route first as that's what they can make most money on?? I don't know - I'm guessing.
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