Poor idle when AC is on

[arrow224]

If the AC button is off, then AC system is off.

If your car still isn't fixed, have a look at your driveshafts, My original front ones were busted, got them replaced with aftermarket ones (not Subaru ones). More vibration throughout the car now.

[Boost]

If the AC button is off, then AC system is off.

If your car still isn't fixed, have a look at your driveshafts, My original front ones were busted, got them replaced with aftermarket ones (not Subaru ones). More vibration throughout the car now.

Interesting. Will have a look

[KiDo_Tuning]

Shav: $20 says I can fix that this week

The AVCS tables ask for 5 degrees AVCS at .35g/rev but 0 degrees at .25g/rev and the idle timing table has flat values, so when the AC is active, the engine actuallys pulls up onto the 5 degrees AVCS with around .42g/rev and the ignition timing makes the engine 'slip' engine revs down until airflow drops and engine load drops below .25g/rev and then it stabilises, before rising again.

Fix is Base Idle Timing tweaked and the AVCS Cruise running less timing advance at 800rpm

[shav]

Shav: $20 says I can fix that this week

The AVCS tables ask for 5 degrees AVCS at .35g/rev but 0 degrees at .25g/rev and the idle timing table has flat values, so when the AC is active, the engine actuallys pulls up onto the 5 degrees AVCS with around .42g/rev and the ignition timing makes the engine 'slip' engine revs down until airflow drops and engine load drops below .25g/rev and then it stabilises, before rising again.

Fix is Base Idle Timing tweaked and the AVCS Cruise running less timing advance at 800rpm

I'll get you to take a look at it when I see you this week Matt. Cheers

[teh_mechanic]

Had exactly the same thing on my 04 auto gt. Idle fine with AC off. Shudders every time Ac compressor kicks in but corrects it in a second or so.

Recently blew my bottom end going up a mountain and as I was pulling the engine out I found the line to the MAP sensor had been blown off by boost, making a leak at the intake manifold. Can't give you a certain answer but there's a good chance this vacuum leak at idle was causing the idle issue so my advice would be have a very good look for any vacuum leaks, if you have access to a scan tool these will show up easily giving you a high fuel trim number.

[KiDo_Tuning]

Forgot to ask if that idle is fixed Shav?

Had exactly the same thing on my 04 auto gt. Idle fine with AC off. Shudders every time Ac compressor kicks in but corrects it in a second or so.

Recently blew my bottom end going up a mountain and as I was pulling the engine out I found the line to the MAP sensor had been blown off by boost, making a leak at the intake manifold. Can't give you a certain answer but there's a good chance this vacuum leak at idle was causing the idle issue so my advice would be have a very good look for any vacuum leaks, if you have access to a scan tool these will show up easily giving you a high fuel trim number.

Idle with AC on is definitely a 'feature' of the stock tune. Static ignition timing on idle timing.

MAP sensor hose blowing off would of caused the engine failure as would have had no closed loop feedback on boost control and no way of hitting a boost cut. Could have had 30+psi and no way for ECU to know

[maj]

MAP sensor hose come off causes erratic idle (+/-more than 500rpm) even without AC on, but sometimes is only noticeable when the car has warmed fully up and comes to a complete stop (eg. traffic lights). AC would accentuate it even further however. I'd consider anything that makes the car shudder as abnormal, usually idle shouldn't hunt any more than 300rpm, with AC off and no heat soak it shouldn't be hunting at all.

I would try to ascertain if there's a problem whilst the AC is off. Check AVCS angle sensors to see if they're in sync, check MAF voltage readings and g/s readings to see if they're within spec (plenty of info if you Google/Youtube this, as well as how to clean them) as well as front O2 sensor readings, and any vacuum hoses connections.

[shav]

Forgot to ask if that idle is fixed Shav?

To be honest, I havent even noticed any idle issues at all since your tune in March Matt. Which tells me you fixed what ever it was back then. As for now, I cant even tell when the a/c kicks in or out while driving. The car is far more friendlier now!