Hi everyone,

 

Noticed a few days ago that my Fabias revs increase when I press the clutch pedal before dropping and increasing to normal. 

 

After using an OBD2 diagnostic it has brought the error code P0171 (bank 1). 

 

I have seen a few forums on this topic but would like to know where to start as I am new to this fault. 

 

I will do simpler tasks myself and if that fails I will pass over to my friend at a local garage. 

 

The car has only done 57k miles and been serviced two months ago.

 

Thanks !

You have an air leak, check the brake servo vacuum pipe, it will be split somewhere.

Okay, does this rule out it being a problem with the EGR valve or the PCV, etc ?

 

What is the best way to check for leaks and is there any problem areas ?

 

Thanks again

Rather than worrying about what may or may not be ruled out, the best idea is to do the check suggested.  It has been thought about and put forward as the most likely problem area, thus saving you time by giving you a shortcut. If it isn't the problem, then is the time to consider other possibilities.

 

Use your eyes and fingertips to look for splits/cracks in the brake servo pipe (the commonest problem area as already mentioned) at the terminations of the hard plastic sections.

This is the sort of thing you may find:

 

I have that code pop up every few thousand miles, I just clear the code and get on with my life. There is no misfiring,, loss of power or anything at all when the code shows so I don't worry about it. It could be just coincidence that you have the revs increasing thing, not related to the code

Excellent. I will report back tomorrow!

 

I didn't realise the brake lines were a common area, noticing most people mentioning the EGR and PCV I have became a little bit cautious of them. 

 

I have noticed the engine does rev harder before the brakes pedal is pressed when stationary - if this means anything ??

 

I really appreciate all your help

It means you have an air leak in the vacuum pipe, fix it.

On it first thing !! 😂

Hi guys. Found this.

 

Is this the crankcase breather hose ? 

 

Could this be the source of the issue ? - it wasn't even attached before I removed the engine cover !

No, that won't be it.

It's just a source of filtered air (as opposed to unfiltered) for the PCV system. If it isn't attached you'll just get a bit of unfiltered air going in there instead, which won't do any harm. the thing it's plugged onto is a one-way valve.

Okay, the other hoses have no obvious cracks and are all connected. 

 

Is there a better way to search for leaks other than visual inspection ?

 

I have cleared the engine light and will take her out for a run to see if it comes back on as a temporary measure

14 hours ago, Wino said:

Use your eyes and fingertips...

 

The splits/cracks often lurk on the underside of the hose fittings, so either use the above suggestion, or phone camera to photograph where the eye cannot get to.

 

You could also use @sepulchrave's suggestion from a nearby thread; find someone who vapes and get them to blow a cloud of vapour into the area while engine is running. Watch for said cloud being sucked in at any points.

Apologies, I have checked with my fingertips too!

 

I will try find someone who capes or smokes then !

 

Would the ECU need recalibrating with VCDS ? I do not have current access to this.

 

Thanks again.

Hi again guys. Had a good look today and can't find anything obvious.

 

No one I know near me vapes - however I have heard spraying carb cleaner on the hose at possible leak spots. Is this a good / bad idea ? 

 

One thing I have noticed is a buildup of some black compound around what I think is the Lambda sensor. Could this be related at all ? 

 

I will update with a photo when the weather calms down a little.

 

Really appreciating all the help i have found on this site so far!

On second look I'm not totally sure what this is. The picture should help ?

That's your oil pressure switch, and it looks like it may be leaking.

I will clean this up when the weather is a little better and see if it gets worse.

 

I presume this is unrelated to my issue ? 

 

I reseated the brake vacuum hose incase it was leaking there. What is the disk like valve in the middle of the brakes vacuum hose ? Could this be the fault ? 

 

 

Yes, oil leak is unrelated.

The disc is a one-way valve; allows airflow towards engine, not towards servo.

After a lot of pondering, tinkering and researching. It would seem that the brakes causing revving was actually a sticking accelerator pedal. Ofcourse this must be unrelated to the engine fault, but the engine fault has not came back since (touch wood).

 

The brakes supposedly overrule the accelerator position as a safety mechanism.

 

As per other recommendations I will get some PTFE spray for the sticking pedal and test and report back.

 

Just updating as may be useful to others with similar brakes/idle revving issues. 

Also check for a hissing noise as soon as the engine is turned off, to determine where the vacuum leak is. It can be difficult to see the split.