Fluctuating And Dipping Rpm

[Dylaan]

I've had my car for a few weeks now and I noticed that every now and then the revs will fluctuate when sitting at idle and usually when slowing down the revs dip really low and sometimes the car will stall.

I've done some research and found lots of information on faulty PCV causing the dipping revs but nothing relating it to the fluctuation.

I mentioned it to my mechanic and he said the car might just need a good run and may have picked up some bad fuel. Now 800kms later it still does it from time to time and it is driving me crazy.

The car is going to the mechanic on Tuesday to get the problem sorted and I wanted to give him an idea of what the problem could be. The car is a 1996 Skyline R33 GTS-T series 2 with 75,000kms on the clock.

Any help would be greatly appreciated.

Dylan.

[stolen-gtr]

you might have already found this during your research, but a common problem for the idle issues is caused by a faulty/dirty AAC valve...there is also a DIY on how to clean it yourself.

I have similar idle issues but mine is ecu related due to an rb20 remap...

good luck!

[mosquitocoils]

AAC valve as already mentioned.. or could be related to an atmospheric-venting blow off valve (if you have one installed)

[Dylaan]

I have heard of the atmo bovs causing the stall issue but my engine it 100% stock. I'll see if I can figure it out myself otherwise i'll pass the info onto my mechanic.

[blind_elk]

Frankly, I don't understand what all the fuss is about erratic idle. It's only idle, FFS. If it were doing it in the middle of an overtaking acceleration, then, yes, you have a right to be concerned, but it's just at idle.

As for the stalling, service the AAC (will probably solve the disaster that is your erratic idle as well).

[Aberax]

I have a similar issue with my car. It running a Haltech E11v2, Nismo 740cc Injectors, and when the aircon is on and i am slowing down to stop at the lights, it always stalls. Another thing it does is it rev hunts when idling at the lights sometimes (generally on warm days), but other times it can be fine.

What do you reckon? AAC Valve too?

[blind_elk]

Probably needs some fine tuning around the idle area of the fuel &/or ignition maps.

[ariandy]

I have a similar issue with my car. It running a Haltech E11v2, Nismo 740cc Injectors, and when the aircon is on and i am slowing down to stop at the lights, it always stalls. Another thing it does is it rev hunts when idling at the lights sometimes (generally on warm days), but other times it can be fine.

What do you reckon? AAC Valve too?

does your AAC connected to your haltech? my friend here also uses haltech, but for AAC he says haltech needs additional controller to control AAC valve opening. Currently his aac valve isn't connected, and having same symptom like you. And also it stalls while parking (maneuvering/driving in slow speed).

Basic function of AAC valve is to increase RPM when there's additional load like aircon and power steering, otherwise it would stall.

Or just try to do simple fix by cleaning your AAC valve, works well on my rb20det, no more stalling issues

[Dylaan]

Frankly, I don't understand what all the fuss is about erratic idle. It's only idle, FFS. If it were doing it in the middle of an overtaking acceleration, then, yes, you have a right to be concerned, but it's just at idle.

As for the stalling, service the AAC (will probably solve the disaster that is your erratic idle as well).

I'm fussed because it sounds annoying and can't be good for the fuel consumption, I want my car to be running top notch

[Mayuri Krab]

Seems like everyone has a idling related problem.

Sorry for hijacking, I have a idling problem that seems to be related to surrounding temperature.

When I drive around during the day (outside temp is ~30+C) the base idling rpm is ~740 to 750, but when I drive around at night (outside temp would be low to mid 20C) the base idle rpm drops to around 680 to 700rpm?

At this dropped idle rpm you can feel a slight vibration from the steering wheel while stopped at the lights.

Any idea on why temperature is causing the drop in idle rpm? Still AAC valve related?

Car has basic mods. turbo back exhaust, POD, R34 GTT SMIC, bleed valve (up to 10psi), SAFC 2 & stock BOV.

Thanks.

Edited February 1, 2010 by Mayuri Krab

[Grimnir]

I have an E6X and get the same idle hunting with my AC on.

Though it doesnt happen all the time. When it does I find just giving the throttle a blip to about 2K RPM and it then idles properly.

[NSNPWR]

Most aftermarket ECUs like the Haltech do not have enough Aux outputs to control things like AAC Valves.......most of the time the idle is jacked up higher to allow for things like Air-con...

[bozodos]

probably the same as my Microtech, though it usually sits around 880rpm - when it starts getting erratic it's usually around the time I'm needing new plugs.

[Dylaan]

turned out to be a faulty oxygen sensor and bad air flow meter. $440 later the problem is fixed.