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350matt
350matt, Engineer
Category: Hyundai
Satisfied Customers: 20780
Experience:  Mechanical Engineer BEng Hons 22 years experience in car engine industry, 10 years in formula 1
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I own a 2015 Hyundai Sonata sport. I had a large pothole in

Customer Question

I own a 2015 Hyundai Sonata sport. I had a large pothole in the car is now idling roughly. Any idea of what it could be?
Submitted: 2 months ago.
Category: Hyundai
Expert:  350matt replied 2 months ago.

Hello

If the car is only struggling to idle now , after the pothole incident then I'd suggest to check for exhaust leaks before the O2 sensor as if this has been experiencing an exhaust leak then it will have been running very rich as the sensor will see the extra air pulled in as fresh / lean fuelling and be adding fuel to compensate.

this can lead to catalyst failure as the extra fuel can re-light inside and melt the catalyst

The best way to find an exhaust leak is to run the engine from cold and feel around the exhaust joints with your bare hands - you'll have about 30 seconds before it all gets too hot and you should feel any escaping gas blowing over your fingers

Customer: replied 2 months ago.
Okay I'll have a look at it and see if it's possibly that. Thanks and have a great day!
Expert:  350matt replied 2 months ago.

no problem

just get back to me on this post

Customer: replied 2 months ago.
Hello Matt. I checked it out and everything seems tight and does not appear to have any leaks.
Expert:  350matt replied 2 months ago.

OK then 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 acausing 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.