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R33 Hunting When Cold

lordsnipe

By lordsnipe,
in General Maintenance

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lordsnipe Community Regular

lordsnipe

Posted
Posted (edited)

Hey guys,

One thing that has become more apparant as of late...

When the car is not up to operating temp yet, sometimes the car will hunt when it's idling at the lights. It doesn't happen all the time but does happen quite often.

Has anyone experienced this and possible solutions?

I've had a search and found a tutorial on cleaning the AAC valve : http://www.skylinesaustralia.com/forums/in...110431&st=0 but it says that the AAC valve only comes into play when the car is warm, not cold... and theres no real problem when warm.

The car is a 1996 R33 GTS-t.

Cheers

Edited by lordsnipe
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insu Rising Star

insu

Posted
Posted

No, I never said the AAC valve doesn't work when its cold. What I said was there is a valve under the AAC which is the cold start valve. It allows more air in at cold idle rather than hot idle, this is why cars rev higher when cold.

The AAC is like a stepper motor, and is controlled by the ECU. It can most definitely affect the car when cold, however it is not the only fix there are numerous reasons why a skyline idle hunts.

If it only affects the car when cold I would start looking at the water temp sender, cold start valve and work my way from there.

Ultimategtr Proficient

Ultimategtr

Posted
Posted

Hey all, i have a bit of a question..

my rb25det idles at like 900ish all the time.. at cold and at warm.. i have read about the AAC vale and to be honest i dont think cleaning thats going to fix it.

My car doesnt have ANY idling issues or anything wot soever.. im basing my theory that either the temp sensor or the cold start valve is buggered..?

What i want to know is that is it possible to clean/fix the cold start valve? is it something that you can adjust by turning with a screw driver?

Thanks :sick:

lordsnipe Community Regular

lordsnipe

Posted
  • Author
Posted
No, I never said the AAC valve doesn't work when its cold. What I said was there is a valve under the AAC which is the cold start valve. It allows more air in at cold idle rather than hot idle, this is why cars rev higher when cold.

The AAC is like a stepper motor, and is controlled by the ECU. It can most definitely affect the car when cold, however it is not the only fix there are numerous reasons why a skyline idle hunts.

If it only affects the car when cold I would start looking at the water temp sender, cold start valve and work my way from there.

Why clean your AAC Valve/ What does it do?

When your RB series motor is warmed up and idling it is your AAC valve which controls the amount of air entering your engine in order to control your idle.

I took that as it only takes effect when warm .. in any case, i'll have a look at your suggestions and go from there.

Cheers

WogsRus Veteran

WogsRus

Posted
Posted

There are acually 3 valves all up in the car. There is the FICD, fast (first) idle controll device, as per nissan fast, this is the little PURPLE plug selenoid, all it does is open and closes to compensate for AC load.

The ACC valve BROWN PLUG, regulates the engine RPM at idle, it controlls the idle to the motor. It work HOT and COLD, any time the car idles. IF this valve is stuffed or dirty, the car will hunt.

There is also a COLD START VALVE, or IACV according to FAST, this is located below the intake plenum and sux to remove, i cut my hands up big time.

This valve controlls the amount of cold air entering the plenum on a cold engine. It houses a sliding disc and a bimetalic strip, which allows for expantion and closes the dick.

This does tend to stuff up, as i found out, it is suppose to be fully open below 20 deg and fully closed after 60 deg C, mine never opened more then half way. I need a new one. $208 from nissan, so i am hunting a second hand one.

If you have hunting, i suspect there are several problems. ONE, your throttle body and butterfly are dirty and not sealing propely. When the cold start valve is open and the butterfly is not closing propely, the acc valve tries to wind the air back, and teh engine will hunt.

OR thhe ACC valve is dirty or fauly, take it all apart and clean WELL with carb cleaner and brushes.

Also possible that the engine temp sensor is a little out of wack, and teh engien is trying to add more/less fuel and the ACC valve tries to compensate for this.

I have had cold start issue for the past 1-2 months, and no one, and i mean no one, can find what is happening, everyhting has been checked, rechecked, and still nothing, Time to swap over all the components and go from there.

insu Rising Star

insu

Posted
Posted
Hey all, i have a bit of a question..

my rb25det idles at like 900ish all the time.. at cold and at warm.. i have read about the AAC vale and to be honest i dont think cleaning thats going to fix it.

My car doesnt have ANY idling issues or anything wot soever.. im basing my theory that either the temp sensor or the cold start valve is buggered..?

What i want to know is that is it possible to clean/fix the cold start valve? is it something that you can adjust by turning with a screw driver?

Thanks :rofl:

Have you adjusted your idle screw?

Baconer Grand Master

Baconer

Posted
Posted

AAC and idle screw, cleaned and adjusted these 2 and solved so many problems:

Idle would eventually sit around 1200rpm after jumping back and forth between 1,000 and 1200 now it sits at 700

Car would have a slight miss on idle (had a lot of idle problems :happy:), now fixed

Vacuum hose (the small thin tube) had a crack down the side of it, had been wondering what the hissing noise coming from engine bay was, now fixed.

Car is so much more responsive now, sounds better overall and performs better. Even if you arent having problems with idle id still recommend cleaning it out if you havent already.

mike_a31 Contributor

mike_a31

Posted
Posted

This is a long shot idea i was told about and i am still a bit skeptical about it but might b worth a try.

Been told when the car is cold the ecu automatically makes the cars idle jump a lil to try warm it up. If the thermostat is jammed open this means the car is gettin fed cold coolant and can take alot longer to get up to temp. SO as such the engine remains cold and the idle jumps a lil to try increase engine temps. Then after a while all the coolant has gone thru the engine and is at a temprature that the engine itself is warm and the idle settles down.

As i said i'm a bit skeptical about that whole idea does sound like one of them bullshit storys a dodgy mechanic might feed you to try hide the fact they have no idea what a cars problem is.

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