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'92 R32 gtst Coughing Idle, Hard Cold Start and Stall W/Clutch In

Hardcase
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Hardcase Rookie

Hardcase

Posted
Posted

Car is hard to start when cold. just have to give it some gas. changed cold start valve did not help issue.

Car coughs at idle about every 1-3 seconds. cleaned and inspected IACV all clean and works. still not helping.

Car stalls with clutch pushed in when coming to a stop when cold. only happens 50% of the time.

Checked TPS all good and reset. 

Car is stock. Brand new OEM coil packs, new spark plugs, new OEM fuel pump and fuel filter. Confirmed no vacuum leaks.

MAF is clean. Idle does not hunt. wiggling the plug to MAF when car is on doesnt affect idle.

Throttle body is clean and cable tightened correctly.

I checked the forums here and what i said above is what people say will fix the issue. The coughing idle is what really bugs me. everything else i can live with.

Car is perfectly fine in every other regard no issues anywhere else.

No i cant just borrow parts from another skyline.

Dose Pipe Sutututu Grand Master

Dose Pipe Sutututu

Posted
Posted

Is the AAC valve blanked off or blocked off? they seem to fail quite a bit and most people just block them off to stop the high idle.

Consequence to this is pretty much what you're describing.

Another way around all this, convert to DBW and throw the IACV, AAC valves all into the bin ;) 

Hardcase Rookie

Hardcase

Posted
  • Author
Posted
 

Is the AAC valve blanked off or blocked off? they seem to fail quite a bit and most people just block them off to stop the high idle.

Consequence to this is pretty much what you're describing.

Another way around all this, convert to DBW and throw the IACV, AAC valves all into the bin ;) 

No its not blocked off in any way

Hardcase Rookie

Hardcase

Posted
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Posted
 

This stupid thing, it sits under your top part of your plenum. A karnt to remove/reach

Iacv Rb20

I just finished installing a brand new one of those today. It didnt help the problem. is blowing into it just making sure it starts to close and works?

Dose Pipe Sutututu Grand Master

Dose Pipe Sutututu

Posted
Posted
1 hour ago, Hardcase said:

I just finished installing a brand new one of those today. It didnt help the problem. is blowing into it just making sure it starts to close and works?

If the motor is cold, you should be able to blow into it, once it warms up it closes up.

When you unplug the O2 sensor does it idle better?

Hardcase Rookie

Hardcase

Posted
  • Author
Posted
 

If the motor is cold, you should be able to blow into it, once it warms up it closes up.

When you unplug the O2 sensor does it idle better?

I forgot to mention that the O2 sensor is also brand new but i will try disconnecting it in the morning. Thanks for the help so far mate.

Dose Pipe Sutututu Grand Master

Dose Pipe Sutututu

Posted
Posted
10 minutes ago, admS15 said:

You forgot samsonas, slipping brah..

fuark.. soz...

Let's try that again

All else fails, CAN O2 wideband, IAT, DBW, DBW pedal, Samsonas,  modern ECU conversion 🤣

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BK Grand Master

BK

Posted
Posted
7 hours ago, Dose Pipe Sutututu said:

This stupid thing, it sits under your top part of your plenum. A karnt to remove/reach

Iacv Rb20

Hey @Dose Pipe Sutututu just to be clear that is an IAC valve, or air regulator valve as the manual calls it, not an AAC valve. The air regulator valve gets a constant 12v on it fed from fuel pump relay and the AAC is pulsed on the ground by the ECU to control the solenoid duty.

To test the air regulator valve as per the manual, without power the valve is only fully open at -20 deg. C, half open at 20 and fully closed at 60. If you 12v power them they are supposed to gradually close fully within 7 minutes. Resistance across terminals is 75ohm at 20c ambient.

Dose Pipe Sutututu Grand Master

Dose Pipe Sutututu

Posted
Posted

@BK perhaps I got the terminology wrong, that device isn't the idle control valve though

The idle control valve sits on the plenum itself. The IAC valve pretty much just has a diaphragm that closes as the motor warms up.

BK Grand Master

BK

Posted
Posted

Yes it does exactly as I mentioned above. It is actually powered to heat up and close, not just engine temp. IACV is probably not a very correct name for it either, but it is certainly not the AAC valve which has the idle screw and solenoid on it as you would know.

joshuaho96 Veteran

joshuaho96

Posted
Posted

Should really be called the fast idle thermo valve, cold start air valve, or something similar that at least indicates that it's associated with cold start air regulation. My advice as I've been working through my own car is to get Nissan Datascan with a Consult cable and take logs when the car is misbehaving. You have to see what the ECU is seeing to understand why the engine is behaving the way it is. The ECU itself has very weak self-diagnostic capabilities, basically the only codes it throws are for things like open circuit/short circuit. All the sensor plausibility stuff is entirely on you to diagnose. How stable are AFRs when the engine stutters at idle? What does the MAF signal look like? Really meditate on the logs before you throw parts at the car. If you're suddenly losing consult cable connection during those drop-outs I would start suspecting the ECU or whatever is supplying power to the ECU.

Hardcase Rookie

Hardcase

Posted
  • Author
Posted
4 minutes ago, joshuaho96 said:

Should really be called the fast idle thermo valve, cold start air valve, or something similar that at least indicates that it's associated with cold start air regulation. My advice as I've been working through my own car is to get Nissan Datascan with a Consult cable and take logs when the car is misbehaving. You have to see what the ECU is seeing to understand why the engine is behaving the way it is. The ECU itself has very weak self-diagnostic capabilities, basically the only codes it throws are for things like open circuit/short circuit. All the sensor plausibility stuff is entirely on you to diagnose. How stable are AFRs when the engine stutters at idle? What does the MAF signal look like? Really meditate on the logs before you throw parts at the car. If you're suddenly losing consult cable connection during those drop-outs I would start suspecting the ECU or whatever is supplying power to the ECU.

I just purchased data scan with cable a few hours ago. Thanks for the help.

 

joshuaho96 Veteran

joshuaho96

Posted
Posted
17 minutes ago, Hardcase said:

I just purchased data scan with cable a few hours ago. Thanks for the help.

 

Once you get logs of the issue feel free to upload it here, I can try and stare at it and see if anything stands out as well.

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