low idle

[computerking]

my fairlady idles at about 750rpm which i guess is normal but sometimes less ie under load and the like if sitting it is ok. If i am on the highway however and doing any kind of speed 100km for example and engage the clutch the call will fight for a bit at about 500rmp then stall. I do not think this is normal what could it be?

[Zwicked]

Check the IACV valve. It is there so when you engage air conditioning or add any load for that matter, it raises the idle.

[nghtrain88]

i have a similar yet kind of opposite problem i suppose.. i have quite a high idle.. around 1000-1100rpms.. i thought this was about normal at first since the car has always idled at this speed.. every once and a while tho it dips down to about 700-750 (recommended) and makes the inside cabin/car vibrate and not idle smoothly, then shortly after returns to ~1000..i thought possibly a motor in the idle air system?

[Zwicked]

A very high idle can be caused by at least a couple things

1. A vacuum leak can do this. Have you ever done a leak test on your intake system to ensure it's intact? 2. The Auxilliary Air Valve used for cold idle increase can be shot and not close3. Likely not this as you say it idles rough when it is at the correct speed, but have you properly adjusted the idle screw? (Unplug AAC, set idle to 600~650 and plug back in)

There may be other things but this is the most common

PS- the rough part of the idle may be some additional issue such as bad injector, plugs, connector corrosion etc

[Wetmyson]

where IS the IAC Valve?

[Zwicked]

The IACV unit in on the rear left of the engine and is a casting that holds the AAC and FICD solenoids. Only available as a complete assembly as new ($300?), but quite a few Nissans of the same vintage use the same solenoids even though the casting is slightly different. They can be found at auto wreckers if you know what to look for. There are 2 types of AAC solenoids, they look similar but have different shoulder so they won't interchange.

Location id marked in red:

(Thanks Robo!)

Item looks like this:



Blue = IACV, Yellow = AAC

2 top bolts, and 1 mediocre hard bolt on the bottom, and one PITA on teh bottom most inward to remove to get this off. Also should use a new gasket when reinstalling as it seals the plenum

[Wetmyson]

thanks a lot! that was very thorough and helpful but i have one more question. a subaru friend of mine says there should be an idle air control sensor somewhere that get can dirty and affect idle. and that you can take it off and clean it and put it back on. is there any truth to that? he says that's how it is on his WRX.

thanks a million

[Zwicked]

Nothing on the VG engine like that I have encountered called that. Do you think he might mean Mass Airflow Sensor? That is located right after the air filter. Unless the filter was damaged and crap got through, they usually don't need cleaning. They are also delicate and really aren't supposed to be touched, but you can buy MAF spray cleaner.Through a combination of other sensors, the ECU takes care of the idle recognition condition and adjustment, but that's where the AAC, IACV and Aux Air valves come in.Other types of engines accomplish things in different ways, so the Subaru could easily be different

[Milo (San Antonio)]

Agree, not really an equivelant of what he is talking about. But he basically means something equivelant to the AAC. It does have a screen inside of it that can be cleaned by just shooting some carb cleaner into it. It can mess with idle a little bit as carbon builds up on the screen creating blockage. It is the other smaller unit that is the middle man between the balance tube and idle adjustment. I would clean both while you are it.

I would just leave the MAF alone like Zwicked stated. They make a MAF cleaner if you really want to clean it. Other than that really there isn't anything else besides cleaning the throttle bodies for carbon buildup as well.

Provided a link to kinda aid you in your quest. Good luck.

Idleadjustment pull - > http://www.twinturbo.net/ttnettech/iaa/iaa.html

Other stuff to check. - > http://www.twinturbo.net/ttnet....html

[Wetmyson]

thanks

[computerking]

thanks here too.

[Zak427]

just to throw it out there, i've had a weak injector casue idle problems and a weak alterantor contribute to it. so don't rush off and spend money before your sure you know whats wrong