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My 2008 Dodge Avenger 2.4 idles up and down when I have

Customer Question
either the ac or heater...
My 2008 Dodge Avenger 2.4 idles up and down when I have either the ac or heater turned on. I recently replaced the ac compressor.
Submitted: 7 months ago.Category: Dodge
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Answered in 24 minutes by:
12/3/2017
Dodge Mechanic: Matt, Engineer replied 7 months ago
Matt
Matt, Engineer
Category: Dodge
Satisfied Customers: 23,315
Experience: Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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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 /propaneor 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.

Air leaks are very temperature dependent as gaps can open up as things expand with temperature so depending on how the leak occurs ( on a hose joint with a clamp expansion will help seal and on a vacuum hose expansion ill make a leak worse) so leaks can be better or worse as the engine heats up.
1 vacuum leak path that you won't find with the above test is if the brake servo is leaking

so try clamping off servo hose to see if this has any effect

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

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Customer reply replied 7 months ago
I know when I remove my gas cap I hear air coming out. I don’t if this would have something to do with it.
Dodge Mechanic: Matt, Engineer replied 7 months ago

Hello

you should get a bit of air rushing in when you open the gas cap, that normal as the system is kept under a slight vacuum

try checking for vacuum leaks as the next step

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Customer reply replied 7 months ago
Should I have the ac/heater turned on while checking
Dodge Mechanic: Matt, Engineer replied 7 months ago

hello

if the issue is made worse by enabling the AC then yes as it should make it easier to find

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Customer reply replied 7 months ago
Would you happen to a diagram showing where the hose are to check? Sorry not a big mechanic person.
Customer reply replied 7 months ago
Can a leaking intake manifold gasket cause this? I hear a hissing sound coming from the left side area of the intake mani fold.
Dodge Mechanic: Matt, Engineer replied 7 months ago

hello

most definitely a leaking manifold gasket can be this issue, try the leak test as I've mentioned to confirm it

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Dodge Mechanic: Matt, Engineer replied 7 months ago

Hi
do you still need help?
Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! If you're not pleased, also let me know because rating bad does not result in a refund, there are better options. Rating now will not close this post nor prevent further replies
Thanks Matt

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