RB20 cutting out on deacceleration - any help appreciated

[Kingsline]

Hi All, 

I recently had a Link G4X installed on my R32 Skyline GTS4 with RB20DET engine. The car keeps cutting out on deacceleration and seems to be worse when warm. 

As soon as the car passes around 3500rpm and you release your foot off the accelerator it will cut itself out and stall unless you keep tapping the pedal to keep the rpm up.

I have removed the Idle Air Control Valve and cleaned it thoroughly and tested the internal spring to ensure its not sticking by putting 12volts into it and it moved freely. Unfortunately it did not make a difference.

I've ordered another secondhand IACV/AAC from the breakers to try as well, but in the interim while I wait I want to see is the issue anything else or something I'm doing wrong.

My knowledge of ECU's is fairly poor, so I'd appreciate any suggestions on this issue! 

Thank you

(Attached MAP and log when parked from cold to hot and cutting out)

R32 GTS4 MAP 403HP.pclx PC Datalog - 2023-07-6 10;00;48 pm.llgx

[Adamw]

Yeah I dont really like the way the base position table has been set up in this, and it is in open loop too, so the ecu cant do anything to correct it.  I think this is likely most of your problem.

Attached is a copy of your map with some changes to your idle settings.  Can you load this in and do a similar log from cold start.  It will likely still need some adjustments but with closed loop working it should give us a better log to work from.  

R32 GTS4 MAP 403HP idle tweaks.pclx

[Kingsline]

Thanks Adam, much appreciated.

[Kingsline]

On 7/7/2023 at 6:45 AM, Adamw said:

Yeah I dont really like the way the base position table has been set up in this, and it is in open loop too, so the ecu cant do anything to correct it.  I think this is likely most of your problem.

Attached is a copy of your map with some changes to your idle settings.  Can you load this in and do a similar log from cold start.  It will likely still need some adjustments but with closed loop working it should give us a better log to work from.  

R32 GTS4 MAP 403HP idle tweaks.pclx 460.65 kB · 2 downloads

PC Datalog - 2023-07-10 4;24;53 pm.zip

 

Hey Adam,

Loaded the tweaked map and have attached the log from cold start to hot.

Its still seems to be acting in the same manner, I also installed a secondhand IACV/AAC and also made no difference.

Have a look at the log and see what you think?

Thanks 

[Kingsline]

15 hours ago, Kingsline said:

PC Datalog - 2023-07-10 4;24;53 pm.zip 3.21 MB · 1 download

 

Hey Adam,

Loaded the tweaked map and have attached the log from cold start to hot.

Its still seems to be acting in the same manner, I also installed a secondhand IACV/AAC and also made no difference.

Have a look at the log and see what you think?

Thanks 

@Adamw did you see this log? Does it look any better.

[DerekAE86]

It looks like you need significantly more air at idle. Once it's warmed up to 80deg closed loop is keeping the idle valve up at 67% to maintain idle.

As soon as you touch the pedal the idle valve is falling back to the base value of 36% which isn't enough air to maintain idle rpm once you take your foot off the pedal so the engine is struggling and stalling because closed loop can't make the adjustment from 36% all the way up to 67% fast enough.

You could change your base table to these values and it should be quite an improvement.

I don't have much experience with RB engines but these values seem rather high. Might be a sign of something else wrong.
Maybe like you initially suspected the Idle Valve is partially blocked or not moving correctly.
Or it could be as simple as the idle adjustment screw isn't adjusted correctly.

[Adamw]

I agree with Derek, just not enough air.  It appears the valve is working correctly as we see the position reduce as the engine warms up.  Setting the base position table as he suggests will work for warm but you are already needing 100% for anything less than 50°C so its not going to have enough air for idle target on cold start.  It might be better to adjust the throttle stop (assuming it is adjustable?) so the idle valve doesnt need to flow so much.  

 

[koracing]

I find an ideal target is 20-25% (or slightly lower depending on IAC resolution) IAC on PWM idle motors at fully warm idle.  This also greatly reduces the tendency to stall when warm as it decreases the sensitivity to stalling when warm as it relies *less* on the ecu to maintain proper idle.