Hunting at Idle?

[SupaFly Skyline]

Hi all, i have an R32 GTSt thats hunting at idle, i took it to a shop and after an hour we traced it to a faulty AACvalve/IAA unit, we swapped mine with a known working one and it fixed the problem, so i tried cleaning mine (fair bit of carbon build up), which didnt fix the problem, so i bought a second hand one form a wrecker, installed it, and the problem was still there, i then reset the ecu as i thought maybe it was "ignoring" the faulty sensor, but this didnt work, i then adjusted the idle to about 2 grand and the "high revs" part of the cycle went for longer, but stilled dropped and fluctuated,

My question is, has anyone had a similar problem and how was it fixed, or does anyone have a suggestion as to what it could be? or is it possible that i was sent a dud IAA?

cheers

[mindflux]

I am not sure what your are asking..

Are you refering to .. When you fire up your car first thing in the morning it revs really high and then drops to liek 2 grand and sits there for a few min before fropping to 800.

If so, this is common as this is the 'Cold Start' feature

[MegaGTS4]

Try this:

Did you clean the one from the wrecker or was it cleaned by them?

Have you tried unpluging the AAC valve to see if there is any change in idle stability after warm up? If idle stabilises then the AAC valve is Dirty or a faulty one.

Make sure the plug is making good contact or has clean terminals on the AAC valve.

Check wiring for breaks/corosion.

If all else fails then you have two faulty AAC valves.

Also these will affect/help idle stability: (for any one else with idle problems, not really your problem)

Check air/fuel ratio's (do a fuel pressure test aswell)

Check ignition timing.

Clean the AFM.

Check vacuum lines and blow by hose.

Check for air leaks in intake pipes.

Basically the idle is controled by the AAC valve after the motor reaches operating temperature, when the motor is cold the valve is closed.

Other factors that affect idle stability after warm up include air/fuel ratio, ignition timing, misfire or in a worst case scenerio cyclinder compression.

Edit: Also the ignition timing, idle speed and CO and HC density (Oxygen sensor) are all inter-related, adjusting/changing one means that you'll need to check the others.

MEGA

[SupaFly Skyline]

Try this:

Did you clean the one from the wrecker or was it cleaned by them?

Have you tried unpluging the AAC valve to see if there is any change in idle stability after warm up? If idle stabilises then the AAC valve is Dirty or a faulty one.

Make sure the plug is making good contact or has clean terminals on the AAC valve.

Check wiring for breaks/corosion.

If all else fails then you have two faulty AAC valves.

MEGA

thanks for the reply, i already tried the things you suggested, but none of them fixed the hunting, although when i disconnected the AAC valve (plug) it kept hunting, ill have to find another one to try i guess

[MegaGTS4]

thanks for the reply, i already tried the things you suggested, but none of them fixed the hunting, although when i disconnected the AAC valve (plug) it kept hunting, ill have to find another one to try i guess

But.... it must be the AAC valve if you said it fixed it once before with the borrowed working one?

The reason that the hunting continued after the AAC was disconnected could be because the valve or spring is binding/seizing in the housing and is making the valve fluctuate causing the unstable idle.

When is it unstable? (All the time or only after the engine warms up)

MEGA

[MegaGTS4]

If it isn't seized or fouling anywhere then you can check the solenoid part of the valve with a multimeter.

There should be 9-10 ohms resistance between the two terminals on the AAC valve.

The plug side (eccs control unit side) is measured in volts and needs to be measured between terminal 1 and ground and it will be:

The plug should look something roughly like this:

.../--...

[.1.I.2.]

Ignition switched on: battery voltage

Cranking engine: 2 to 3 volts

Idle when cold: 6 to 7 volts

Idle when warm: 8 to 10 volts

Sorry I couldn't be more helpful, if you lived in my home town I would try to fix it for you.

Edit: I have attached a pic of idle adjustment info. (sorry about the quality)

MEGA

[SupaFly Skyline]

thanks a lot for all your time and help Mega, much appreciated, i think it ill have to try and get my hands on another unit sometime early next week and fingers crossed all my problems will disappear