R34 GTT idle problem

[silviaz]

1 hour ago, MBS206 said:

How old is the battery, it's more likely your battery is on its way out.

It's new almost. Under a year old i think and I've tested it twice at supercheap

Edited February 4 by silviaz

[GTSBoy]

3 hours ago, silviaz said:

Drops to 9.76v while cranking then quickly goes up to 14.5v

Anything above ~9.5V is acceptable. The higher the better, but it will almost always drop to at least 10.5V, if not lower, even with a new big battery and everything else being good.

9.76 is not a concern. If it goes below 9, you'd be sure that there's a problem with either the battery or the connections.

[silviaz]

34 minutes ago, GTSBoy said:

Anything above ~9.5V is acceptable. The higher the better, but it will almost always drop to at least 10.5V, if not lower, even with a new big battery and everything else being good.

9.76 is not a concern. If it goes below 9, you'd be sure that there's a problem with either the battery or the connections.

Ok guess I can rule out the battery, probably even the starter and alternator (maybe) as well. I'm gonna clean those leads and see what happens if it's still shit I might take it to an auto electrician. Unless the immobiliser is that f**king heavy, but it shouldn't be. 

If I start the car every day, starts up perfectly never an issue.

Isn't 12v low, shouldn't it be around 12.5v?

Edited February 4 by silviaz

[GTSBoy]

Car should sit at 12.2 or more, maybe 12.6 or 12.7 when fully charged and happy. If there is a decent enough parasitic load then it will certainly go lower than 12.2 with time. You can't beat physics.

[MBS206]

12.8 for a great condition, fully charged battery.

If the battery will only ever properly charge to about 12.2V, the battery is well worn, and will be dead soon. When I say properly charge, I mean disconnect it from the car, charge it to its max, and then put your multimeter on it, and see what it reads about an hour later.

Dieing batteries will hold a higher "surface charge", but the minutest load, even from just a multimeter (which in the scheme of things is considered totally irrelevant, especially at this level) will be enough over an hour to make the surface charge disappear.

 

I spend wayyy too much time analysing battery voltages for customers when they whinge that our equipment (telematics device) is causing their battery to drain all the time. Nearly every case I can call it within about 2 months of when the battery will be completely dead. Our bigger customers don't even debate it with me any more ha ha ha.

A battery at 12.4 to 12.6 I'd still be happy enough with. However, there's a lot of things that can cause a parasitic draw in a car, first of which is alarms and immobilisers. To start checking, put your multimeter into amps, (and then connect it properly) and measure your power draw with everything off.

Typical car battery is about 40aH. Realistically, you'll get about half this before the car won't start. So a 100mA power drain will see you pretty much near unstartable in 8 days.

[MBS206]

On 2/2/2025 at 1:26 PM, Dose Pipe Sutututu said:

Ohh even easier.

 

Go dial up 700rpm on the hand controller. Rip off the TPS plug, wait till the idle drops and then adjust the IACV screw so it's just a tad below the target on the hand controller (say 650rpm), plug the TPS back in and idle will climb back to target.

Done.

On the R34 can't you just unplug the IACV? This is the way I've always done it on the R33.

Disconnect IACV, get it idling around 650rpm, and then do a power reset on the ECU to get it to relearn idle (factory ECU).

 

The big reason no one has touched on as to why you'd want to get the base idle right, is that it means the computer needs to make smaller adjustments to get a good idle at 700-750rpm.

 

Also, cleaning the IACV won't normally make the car suddenly idle lower or higher. The main issue with the IACV gumming up is that the valve sticks. This means the inputs the ECU gives, aren't translating to changes in air flow. This can cause idle choppy ness as the ECU is now needing to give a lot of input to get movement, but then it moves too far, and then has to do the same in reverse, and it can mean the ECU can't catch stalls quickly either.

Edited February 4 by MBS206

[silviaz]

53 minutes ago, GTSBoy said:

Car should sit at 12.2 or more, maybe 12.6 or 12.7 when fully charged and happy. If there is a decent enough parasitic load then it will certainly go lower than 12.2 with time. You can't beat physics.

Ah right. Maybe my rb just loves chewing through batteries lol.

[Dose Pipe Sutututu]

1 hour ago, MBS206 said:

On the R34 can't you just unplug the IACV? This is the way I've always done it on the R33.

Oh yeah forgot to also mention need to also unplug the IACV as well. Thanks for the reminder @MBS206

Unplugging the TPS takes it out of closed loop so you're able to screw down the IACV without the ECU trying to add/subtract timing to maintain the idle (not sure PowerFC can even do this, but Nistune and the OEM definitely does)

[silviaz]

I noticed something. On the tps sensor and the sensor behind the adjustment screw is adjusted towards the far left. Are these screws supposed to be centered? (this sensor was in the same position before the tune as well) 

Also attached a photo of where my car usually idles at when warm (sometimes a tiny bit above that). I think I might have screwed up the calculation and it might have better than I thought lol at 750rpm still not 650rpm though.

 

 

 

Edited Thursday at 12:28 AM by silviaz

[joshuaho96]

5 hours ago, silviaz said:

I noticed something. On the tps sensor and the sensor behind the adjustment screw is adjusted towards the far left. Are these screws supposed to be centered? (this sensor was in the same position before the tune as well) 

Also attached a photo of where my car usually idles at when warm (sometimes a tiny bit above that). I think I might have screwed up the calculation and it might have better than I thought lol at 750rpm still not 650rpm though.

 

 

 

TPS sensor needs to be adjusted such that idle voltage is 0.45V, then relearn the TPS if applicable. From what I recall in the R32 GTST and similar ECUs they care far, far more about the actual TPS closed switch but later models seem to only keep track of voltage.

[GTSBoy]

On R32s etc the variable resistor of the TPS is pretty much only for the auto trans CU. The switch is the idle position.

Yes, later ones want to see pretty close to 0.45V to declare idle position.

[Dose Pipe Sutututu]

8 hours ago, silviaz said:

750rpm still not 650rpm though.

Good enough tbh 😀

[silviaz]

1 hour ago, Dose Pipe Sutututu said:

Good enough tbh 😀

Yeah was thinking that. I've had the car go lower idle possibly around 650rpm every once in a long time after pouring fuel and would sound quite rough like a misfire, almost like it's shit fuel or something but who knows.

Edited Thursday at 10:36 AM by silviaz