Hi all,

 

New member here, having bought an 08 petrol fabia a few months ago and it has now started doing this when idleing, likelihood of this being the mass air flow sensor or something more difficult/costly?

 

 

Cheers for any help.

If you use words this is commonly described as surging at idle and it's usually caused by a leak in the vacuum pipework or the intake system.

11 minutes ago, sepulchrave said:

If you use words this is commonly described as surging at idle and it's usually caused by a leak in the vacuum pipework or the intake system.

Ok, thanks for the help, I'm a new car owner so am not aware of all the correct terminology. How simple is something like that to fix? Sounds like a job I'm not going to be able to do by myself

 

It's tricky to find leaks, you need to know where to look and if you don't know what anything is and it just looks like a confusing jumble of wires and pipes under the bonnet with a metal box nestling in the middle of it all then you stand little chance.

On countless occasions we've told people where to look for the problem and they just come back and say that everything looks fine.

So it can be an exercise in frustration coaching non-technical minds to fault find something they don't understand.

I'm an engineer so I am somewhat technically minded but I'm realtively new to cars not having needed one until recently so although I can point at and name most of the engine bay I can admit trying to find a leak is outisde of my current abilities as I won't know which pipes and hoses are the likely culprits.

 

I shall take it to a garage, thanks for you help

Before going to a garage please check the air filter pipes and clips to see they are seated correctly i have seen so many issues like this were people change filters etc and do not seat pipes and the clips properly  after, some garages just loosen and retighten pipes and clips  and then car runs ok but charge you a fortune  for many items "that were faulty"

I changed the air filter when I got the car a couple of months ago and haven't touched it since, I'll check all the clips on the air filter pipes and the filter housing  that I can identify to see if things weren't re-attached properly and have rattled loose, I also have an obd reader arriving tomorrow which might help confirm it's a vacuum leak.

 

Thanks for the suggestion

Be aware that an OBD reader may indicate a problem with the MAP sensor since that’s the only sensor it can use to detect a leak. Needless to say it won't be the MAP sensor that's at fault.

Just been out to the car to change a bulb and checked the engine bay and ran it while I was there to see if I could hear anything. revs were sat quite happily at 900-1k and not going anywhere. The video in the original post was after a 120 mile motorway journey yesterday, is there something that would explain why it behaves that way when wamn but normally when cold?

 

19 minutes ago, sepulchrave said:

Be aware that an OBD reader may indicate a problem with the MAP sensor since that’s the only sensor it can use to detect a leak. Needless to say it won't be the MAP sensor that's at fault.

 

Cheers for that if it says MAP sensor I'll know what it means and will let garage know if it ends up at one

Garages are mongs, they just change whatever the reader says is wrong, they play parts bingo with your money, next it would be the throttle body, then the pedal assembly, then the ECU.

I know how their primitive reptile brains work, they don't do the job to fix your car, they do it to get paid, fixing your car is incidental.

Edited 14 March, 20215 yr by sepulchrave

Looks like it being rough when warm but fine when cold confirms your vacuum leak theory. I'll have a go at visually inspecting stuff myself and hope to identify the problem hose.

If possible I would like to fix myself as I like projects like this and a car is a new playground for me, garage would be last resort if I can't fix it

 

Is yours a 6-valve (60bhp) or 12-valve (70bhp) HTP?

 

On either the brake servo vacuum hose is a favourite for leaking at the connections to the non-return valve not far from where it leaves the inlet manifold.

On the 6-valve variant there's another hose worth well looking at, but I won't bother describing it until I know whether you have that engine variant.

1 minute ago, Wino said:

Is yours a 6-valve (60bhp) or 12-valve (70bhp) HTP?

I have the 12v variant.

 

Not sure if this was the only issue but it definintely wouldn't help the air leak situation, I would like to preface this by saying my more knowledgeable mate who was there at the time was responsible for swapping the airfilter whilst I was doing the pollen filter.

The back left screw missed the mounting hole... This is now fixed.

Unfortunately, air leaks upstream of the throttle body won't be relevant, they'll just let unfiltered instead of filtered air in.

I have had a feel around the non-return valve (or atleast what I believe it to be and have circled in red) and cant feel anything when the car is running, I don't think I'd have expected to though tbh

 

 

I will give it a run tomorrow to get the engine hot, when I do what should I do to test afterwards if the leak is there, I have read that spraying stuff onto the hoses and listening to hear if the revs change is a good idea, is that what you would recomend?

 

Dude, that hose is covered in elec-chickens tape! It's bound to be split to hell under there. Fix it.

Ok noted, that would explain it, I thought as it was all covered maybe it's supposed to be that way. I was wrong.

 

I assume the previous owner also discovered it was leaking and this was their fix for it.

 

How easy are these hoses to swap out myself/with a mate?

Peel off the tape either side of the non-return valve and re-do it carefully with gaffer tape.  See if the fault goes away.  Always a good idea to be sure of a diagnosis before spending hard-earned.

Yeah agreed, I assume this will probably need replacing sooner rather than later even if the current bodge job is still holding, so if it's not the problem might as well do it at the same time once I've identified the source of the current leak

It will be leaking, that tape is flapping about and the adhesive liquifies at under-bonnet temperatures, the only stuff that's airtight is self-amalgamating tape and that doesn't really like the heat either.

Reasonably easy to swap out, there might be an awkward clip at the engine end, and removing the servo end is much easier if you pump the brake pedal a few times before trying.  Once you have the tape off you may be able to read a part number straight off it.  Written all the way along the hard plastic sections repeatedly.

Cheers, I'll peel off around the nonreutrn valve and replace with gaffer tomorrow then give it a bit of a motorway run to warm and see if it's fixed, if it is I will replace the hose soon when I am able to, if not, I'll do some more hunting around I guess. Replacing that hose soon definitely seems like a smart move.

I assumed the tape was factory, it looked too well applied for a bodge but after some googling it is defininitely not factory.

 

Cheers for all the help today and I'm sure I'll be back tomorrow, even if it's just to give an update that the non return valve is the leak and the problem has been found.

Is there any recommended palces to buy repalcement parts like this?

You'll only be able to buy genuine I think, so TPS, dealership parts counter, or someone like Mike at Coverdale Carparts, a forum sponsor: Home | Coverdale Car Parts

Phone him tomorrow.

 

Come to think of it, any of those places will be able to find the correct part number without you telling them anything more than your reg number, so no need to dig under too much tape.

Cheers, there is a TPS super close to me, I'll give them a ring in the morning and see what they say. I'm thinking I might replace that before spending anymore time looking for a leak, that way if this is the culprit I won't have wasted any time and it definitely needs doing anyway.

There might be another leak as well but I can hunt for that after I've repalced this if the problem persists.

Edited 14 March, 20215 yr by BrumTom_