Poor idle when AC is on

[Boost]

Hi guys,

This is my first time owning a Subaru. It's a 2004 Liberty GT wagon, automatic.
I've tried searching the forum on the topic of poor idle when the ac is no with no luck.

Can someone please shed some light as to why or what is causing this. It idles fine when the AC is off but when its on, the idle seems to be fluctuating up and down.

Cheers guys.
Steve

[kiahatsiu]

It does that as the compressor cuts in and out, though it might be worth looking for air leaks.

[Boost]

I can here the compressor kicking in and out but surely the idle isn't supposed to be that rough is it ??

[zch91]

I've got exactly the same car, the idle does change obviously but the computer corrects it pretty much straight away, it's never rough.

Maybe the compressor is on the way out, or another underlying problem. Just my thoughts, I am not a mechanic.

[kiahatsiu]

Where do you live dude?
And Zach, when did you move to Darwin?

[zch91]

Just arrived this week actually. Moved here for work

[KiDo_Tuning]

Hi guys,

This is my first time owning a Subaru. It's a 2004 Liberty GT wagon, automatic.
I've tried searching the forum on the topic of poor idle when the ac is no with no luck.

Can someone please shed some light as to why or what is causing this. It idles fine when the AC is off but when its on, the idle seems to be fluctuating up and down.

Cheers guys.
Steve

All Subarus have a jerky idle with the AC on in stock form, even the 2012 WRX/Liberty/Forester etc

[Ben]

If it's properly hunting (like nearly conking out), it's going to be an o2 sensor. Don't replace it with an old version, get a new version from the link below.

viewtopic.php?f=38&t=12832

Many a forum member with a 2.0T has explored this and some never get to the bottom of it.

My car was hunting badly, now it's quite rare and nothing like it was. Usually only happens in 30+ heat and normally purrs like a kitten. O2 sensor made all the difference, it was horrible before.

[Boost]

Where do you live dude?
And Zach, when did you move to Darwin?

Hi Ian. I live in Sydney

[Boost]

If it's properly hunting (like nearly conking out), it's going to be an o2 sensor. Don't replace it with an old version, get a new version from the link below.

viewtopic.php?f=38&t=12832

Many a forum member with a 2.0T has explored this and some never get to the bottom of it.

My car was hunting badly, now it's quite rare and nothing like it was. Usually only happens in 30+ heat and normally purrs like a kitten. O2 sensor made all the difference, it was horrible before.

It doesn't hunt to point where its about to stall but its jerky enough to feel the car shake..

[Boost]

Just an update.

I've noticed it only idles weird when its in drive. In park its fine.
I'm assuming this would eliminate an 02 sensor problem as it wouldn't matter whether its in drive or park.
Blocked filter banjo or dirty MAF ?

[zch91]

Mine was doing a similar thing about a month ago (idling very low/nearly stalling in D, fine in P), lasted a few days and was fine after that, haven't had any more issues.

I know that doesn't really help, but at least you know you're not alone

[shav]

The most common problem with Subaru air con's is that when they get serviced, the air con guys fill them right up to the top over pressuring the system. This in turn makes the clutch on the compressor turn on and off more erratically and effecting your idle. Get your air con guy to remove some gas from your system, and tell him not to fill it to the top but perhaps 97% or so. You will find the erratic feeling of the air clutch will calm right down and only engage when its required.

I found this out on my last Subaru wagon and now this Lib GT.

[Boost]

The most common problem with Subaru air con's is that when they get serviced, the air con guys fill them right up to the top over pressuring the system. This in turn makes the clutch on the compressor turn on and off more erratically and effecting your idle. Get your air con guy to remove some gas from your system, and tell him not to fill it to the top but perhaps 97% or so. You will find the erratic feeling of the air clutch will calm right down and only engage when its required.

I found this out on my last Subaru wagon and now this Lib GT.

I initially thought it was idling weird when the AC is on but its doing it in Drive even with the AC off.
Unless the compressor is still On even with the AC off ?

[shav]

The most common problem with Subaru air con's is that when they get serviced, the air con guys fill them right up to the top over pressuring the system. This in turn makes the clutch on the compressor turn on and off more erratically and effecting your idle. Get your air con guy to remove some gas from your system, and tell him not to fill it to the top but perhaps 97% or so. You will find the erratic feeling of the air clutch will calm right down and only engage when its required.

I found this out on my last Subaru wagon and now this Lib GT.

I initially thought it was idling weird when the AC is on but its doing it in Drive even with the AC off.
Unless the compressor is still On even with the AC off ?

I couldn't answer that with a certainty. I reckon it's possible especially if the compressor is chock block full of gas that its forcing the clutch to engage.

Even if in drive or park, my car was still running as if it I had the foot on the accelerator and stalling the car up, on and off.