R32 GTS (RB20DE) Injectors Replacement

[MBS206]

2 hours ago, GabsReDeal said:

My bad, I unplugged the one underlined in red instead of yellow before.

With the car started, after unplugging the IACV (the one underlined in yellow), it idled at around 400/500 for 3 seconds before stalling. Attempting to start the car without the IACV will not start the car.

 

It does stutter and sputter for around 5 seconds before dying. However, immediately after starting it, you can already hear some slight sputters from the exhaust.

 

It won't start with the AFM unplugged. If it is when the car has already started, it stalls in a few seconds.

 

Yesterday, I did take some logs using Nistune of 3 scenarios.

1. Car idling till it stalls
2. Car idling and unplugging the IACV
3. Car idling and removing the AFM

I also have some previous logs of when the Car is idling till it stalls and when driving and it cuts. I am not really knowledgeable enough to understand what to look for.

After every test, car idles rougher and rougher, until I have to stop. It will be fine the day after.

Your IACV is set to idle too low.

You need to adjust it via the screw Duncan mentioned.

From memory it should be 650rpm with the valve electrics unplugged.

What is it trying to idle at with the IACV plugged in?

[GabsReDeal]

On 25/08/2025 at 8:58 AM, Duncan said:

You've mentioned the IACV, does it have an AAC valve and have you adjusted it at all (ie, screw the idle adjust screw all the way in, then back it out a couple of turns until idle is stable)?

I never touched it, it should have. I'll try to give it an adjust.

On 25/08/2025 at 11:21 AM, MBS206 said:

What is it trying to idle at with the IACV plugged in?

With IACV plugged in, it idles at around 1120RPM on average. Max 1200 RPM, Minimum 1025RPM before it starts dropping right before stalling. Took the data from the Nistune logs.

[Duncan]

OK, if it idles at 1000+ with the AAC, its not an idle airflow problem. The cold start valve just gives extra air when the engine is cold, but you have enough air without it to idle at 1000.

I think you are back to a fuel problem, sorry. Can you see the fuel pressure staying constant or does it drop as the revs drop to a stall?

 

[GabsReDeal]

On 25/08/2025 at 2:06 PM, Duncan said:

OK, if it idles at 1000+ with the AAC, its not an idle airflow problem. The cold start valve just gives extra air when the engine is cold, but you have enough air without it to idle at 1000.

I think you are back to a fuel problem, sorry. Can you see the fuel pressure staying constant or does it drop as the revs drop to a stall?

 

In my head it does make sense to be a fuel problem since that is what I touched when cleaning the system.

When I was testing with the fuel pressure gauge, the pressure was constantly 2.5 bar with the FPR vacuum removed. When stalling, the pressure was going up to 3.0 bar (which is how it should be on ignition).

[MBS206]

6 hours ago, GabsReDeal said:

In my head it does make sense to be a fuel problem since that is what I touched when cleaning the system.

When I was testing with the fuel pressure gauge, the pressure was constantly 2.5 bar with the FPR vacuum removed. When stalling, the pressure was going up to 3.0 bar (which is how it should be on ignition).

If as it's stalling, the fuel pressure rises, it's saying there's less vacuum in the intake manifold. This is pretty typical of an engine that is slowing down.

 

While typically is agree it sounds fuel related, it really sounds fuel/air mixture related. Since the whole system has been refurbished, including injectors, pump, etc, it's likely we've altered how well the system is delivering fuel. If someone before you has messed with the IACV because it needed fiddling with as the fuel system was dieing out, we need to readjust it back.

Getting things back to factory spec everywhere, is what's going to help the entire system. So if it idles at 400rpm with no IACV, that needs raising. Getting factory air flow back to normal will help us get everything back in spec, and likely help chase down any other issues.

Back on IACV, if the base idle (no IACV plugged in) is too far out, it's a lot harder for the ECU to control idle. The IACV duty cycle causes non linear variations in reality. When I've tuned the idle valves in the past, you need to keep it in a relatively narrow window on aftermarket ecus to stop them doing wild dances. It also means if your base idle is too low, the valve needs to open too much, and then the smallest % change ends up being a huge variation.