Idle Stalling Issue

[heslo]

Just yesterday my GTS-t started developing weird stalling issues. I turned the car on, revs sat where they normally would (~950) for a second and then dropped to around 300ish and bounced back up to 950 again. It did this repeatedly until it stalled. Started the car again, same thing. Started again and had massive trouble starting it, had to step on the accelerator to get it started. This time when it came to life, no idle hunt, just a nice clean 950 RPM.

Later in the day, same thing occurred however this time I found that if I stepped on the gas and held it at say 2000 RPM, the revs would not drop, they would stay where they are supposed to. I got the car running and then took it for a spin around the block at which time the engine check light came on. I turned around, took the car back home and just before I arrived it went off again and haven't seen it come on since.

Today I changed the spark plugs thinking they may have had something to do with it as they were due for a change but that didn't alleviate the problem. I'm starting to think now maybe the AFM or the TPS might be on the blink but I honestly don't know where to start.

One more thing of interest is that a few weeks prior to this starting I cleaned the AAC valve, I thought that this may have done something but then I thought if I had caused something to go wrong, problems would have started straight after, not now after putting roughly 1000 more k's on the clock.

The car is mildly modded with a PowerFC, cam gear, boost controller, exhaust and pod, please if anyone could help or has any ideas, I'm open to suggestions

Thanks

[mad082]

could also possibly be the o2 sensor is a bit dodgy.

[heslo]

Well I was told at my last service that the O2 sensor was actually stuffed so I don't think that it would just start like this out of the blue as the PFC is on a closed loop anyways

[lows_13]

I had a similar problem with my car, i cleaned the AAC valve, did everything. Last of all disconnected the O2 sensor and everything ran sweet. I then changed the O2 sensor and re-connected it up again and problem fixed.

[Craved]

Well I was told at my last service that the O2 sensor was actually stuffed so I don't think that it would just start like this out of the blue as the PFC is on a closed loop anyways

closed loop means using the O2 sensor..

so maybe disable that feature and test ..

[heslo]

Sorry, I meant it wasn't using the closed loop function. Doesn't matter anyways, found the problem. Looks like it was a TINY slit in one of the vacuum hoses coming out of the AAC valve. Got a new piece, switched it over and hey presto, works a treat!

Thanks for the input anyways fellas, greatly appreciated!

[Mike_]

I'll keep that in mind, I've had the same problem the last couple days but I noticed its only happening in the heat (I'm in Adelaide too). At night or early morning its fine, but turn it on during the day when it hasnt been running for a few hours and it wouldnt stay on.

I was worried it may have been something more sinister.

I'll check my aac hoses as you've done first, also ill give the valve a clean, but definitely post again if you have more problems as the heat comes in!

Edited September 18, 2006 by Mike_

[paulr33]

02 feedback would never cause wierd idle hunting/stalling like that

[lows_13]

Mine did, the O2 sensor was faulty, and was making the car run really lean to the point where it was starving the engine fuel at idle. I performed the test by using the LED on the back of the ECU, replaced the O2 sensor, all good.

[Nozila]

would a stuffed o2 sensor caused idle hunting issues at all though??

[paulr33]

i still dont see how it could cause it, but according to the service manual it can. so im wrong

[paulr33]

service manual page

i recall reading somewhere it only rich or leans it out a small percentage its not a massive change so it would be odd to make it stall

but the manual says so, so it must be the case. well you can always unplug it, the car should work fine, it will just waste fuel

[lows_13]

There are basically two tests you can perform, unplug the O2 sensor and see whether it runs better. Also there is the ECU test which is quite easy to perform.