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Matt
Matt, Engineer
Category: Australia Car
Satisfied Customers: 21988
Experience:  Automotive Engineer for 20 years, BEng hons degree,
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Hyandai elantra stalling when stopped at lights. when turned

Customer Question

hyandai elantra stalling when stopped at lights. when turned back on starts but sometimes begins hunting up to 1750 revs
JA: Is the check engine light on? Does the car stall at idle or when driving?
Customer: no engine light, no it doesn't stall when driving
JA: What year is your Elantra?
Customer: 2006 but it think its the end of that model.
JA: Are you fixing your Elantra yourself? What have you tried so far?
Customer: Unfortunatley I dont know much about cars. The Hyandai people were I live had a go but no luck (I assume they used the computer and couldnt find anything. My own mechanic has had two cracks... but no good
JA: Anything else you want the mechanic to know before I connect you?
Customer: my mechanic used terms like carboned up and idling something... sorry
Submitted: 6 months ago.
Category: Australia Car
Expert:  Matt replied 6 months ago.

Hello
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 or brake cleaner 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.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

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

It’s also worth cleaning the MAF sensor wires, as they can get coated with dirt over time which then offsets the reading
Use some contact cleaner or brake cleaner to spray onto the wires to remove the dirt – on no account touch the wires with anything as they are very fragile