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Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 20364
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Evening all I have a 2012 fabia vrs and was concerned about

Customer Question

Evening all
I have a 2012 fabia vrs and was concerned about the 3/4 litre of oil it was burning a month.
So when it went in for its service I had a compression test done to which the results were fine,also replaced the plugs.
Since then my engine management light has been on and the car has been over revving at idle,had a guy at work clear the faults to which it was coming up as P0507 code - higher than expected revs!!
Cleared the fault again this afternoon but the engine light has come on again tonight.
Am sorry I had the compression test done now cause the car was ok before.
Any ideas?
Submitted: 1 year ago.
Category: Car
Expert:  Matt replied 1 year ago.

This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.
As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.
Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

Might also be worth cleaning out the throttle body as these get clogged up with carbon and some brake cleaner washed through helps free things off.

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.
if the engine condition is the same then chances are the meter or the connection to it is faulty

Air leaks are very temperature dependent as gaps can open or close up as things expand with heat, so the weather and engine temperature can effect them.

This leads them to be quite intermittent in the case of mild leaks

its also worth cleaning the airflow meter by removing it from the car and spraying the exposed sensor wires inside the tube with a brake or switch cleaner - ensure that the cleaner is one of the old fashioned, non Eco type that does not leave a residue

On no account touch the sensor wires with anything physical as they are extremely fragile
Expert:  Matt replied 1 year ago.

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