Rough idle, surging, erratic but only when stopped at lights

[zch91]

Hey guys..

Over the past few weeks (maybe even more than a month I can't remember) my car has been idling weird when stopped at traffic lights...

Normally it'll idle at around 700rpm no worries (as viewed on my ECUdatascan) but lately it jumps from 700 down to 500 and back up again at a constantly.. Sounds abit like a v8 with a massive cam.

Drives normal and seems to boost fine when driving around.. Just happens when stopped at traffic lights (in D with brakes on)

I have tried without aircon etc and makes no difference so it's not the AC compressor, not that it kicks in/out as fast is this anyway.

Any ideas? Someone mentioned it could be a vac leak.. what PITA that would be.

I've cleaned the MAF with contact cleaner (thanks HKS filter for the dust) and reset the ECU and still doing it..

The car is an MY04 GT 5EAT

Cheers

[dr20t]

Vacuum leak
Dirty maf
Faulty front 02 sensor

[zch91]

Thanks for your reply Mick.

Any clues for common spots for a vac leak? I don't have any equipment to test it apart from pulling stuff apart.

Already cleaned the MAF and hasn't helped at all

O2 sensor has always been in the back of my mind since I owned the car, since I know they're prone to failure I've always considered swapping it out but never had any symptoms of it being buggered.. Might grab one from G88 and see if that helps.

[04GTLIB]

Zach.

Ours had identical issues and it turned out to be an O2 sensor. See Phat, as I'm pretty sure he has these in stock.

Cheers,
Rusty.

[dr20t]

No probs at all

For Vacuum leak check obvious places like joins, all rubber hoses - common one is the bov return hose either at bov end or manifold end. Also check vacuum nipples on some of the ancillary sensors

While you're at it check the map sensor (hanging on metal bracket attaching to the inlet manifold located around / behind the power steering pump). Might be blocked up a little or vacuum hose split to it etc

So many different variables its hard to diagnose but I'd check those things

Mick

[zch91]

Thanks Russ, have just purchased one from G88, hopefully fixes it right up

Thanks again for your input Mick, I will spend a bit of time today looking at it, hopefully I find something

Will report back any findings!

Cheers

[Ben]

Thanks Russ, have just purchased one from G88, hopefully fixes it right up

Thanks again for your input Mick, I will spend a bit of time today looking at it, hopefully I find something

Will report back any findings!

Cheers

Mine has idled perfectly since replacing the 02 sensor, pleases me a lot. Hope it works for you as well mate!

[zch91]

Did you have the same symptoms?

Anxious to receive the sensor now

[NRV155]

How much are his sensors? Im going there tomorow.

[zch91]

According to his vendor page $250, was $275 for me (Maybe more because I live in Darwin)

[Hobba]

According to his vendor page $250, was $275 for me (Maybe more because I live in Darwin)

These can be had on RHDjapan.com for little over $100 delivered.

http://www.rhdjapan.com/subaru-oem-air- ... 2006-64493

[zch91]

Is it the same as this one though?

viewtopic.php?f=38&t=12832

[Hobba]

Is it the same as this one though?

viewtopic.php?f=38&t=12832

Yep its the updated one, installed one myself from there about a month ago.

[maj]

Mine always has moved between 700-1000 when the engine is hot at lights, even with replaced MAF sensor.

On the rare occasion though, usually not long before it's due for a service, it drops down to 500-1000 and becomes more erratic.
If I plug in my tactrix cable and check the learning tables, they look mostly okay; IAM at 1.00 but a few corrections at certain RPM, nothing really out of the ordinary though.
As soon as I reset ECU though and let it relearn, erratic idle goes away and it behaves again for a long time.

I also get in the habit of resetting ECU after the car comes back from service at the dealer.

Good first precaution would be to reset the ECU and check codes before jumping to MAF or O2 sensor conclusions. Vacuum leaks are always worth looking for though, especially if your MAF has accidentally been disconnected (dealer did that once to me).

[zch91]

Thanks for your post Michael. I've tried ecu reset and cleaning the AFM with no avail. Have already ordered the O2 sensor which should arrive over the next few days hopefully.

Will report back when I know more.

Cheers,

Zach