R34 GTT idle problem

[Dose Pipe Sutututu]

4 hours ago, silviaz said:

Apexi, though I'm not comfortable with setting the idle, knowing me I'll f**k it up lol.

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.

[silviaz]

2 hours ago, 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.

That sounds pretty easy actually haha. But is there a reason why the tuner didn't do this? It's not like I've got a cammed 500kw rb25 neo. 

 

Also the tps plug is different on the rb25det neo and the r33 for example, I guess I'd plug out the loom which is this end? There's also 2 connectors. 

Edited February 2 by silviaz

[Dose Pipe Sutututu]

1 minute ago, silviaz said:

is there a reason why the tuner didn't do this?

A high case of cbf.

Car runs, idles fine, not touching it.

 

[silviaz]

Just now, Dose Pipe Sutututu said:

A high case of cbf.

Car runs, idles fine, not touching it.

 

I suspect that to.

[Dose Pipe Sutututu]

6 minutes ago, silviaz said:

Also the tps plug is different on the rb25det neo and the r33 for example, I guess I'd plug out the loom which is this end? There's also 2 connectors. 

Unplug both, it causes the idle closed loop condition to not be satisfied 

[silviaz]

Just now, Dose Pipe Sutututu said:

Unplug both, it causes the idle closed loop condition to not be satisfied 

Ok will keep in mind. Appreciate your help!

[soviet_merlin]

9 minutes ago, Dose Pipe Sutututu said:

A high case of cbf.

Car runs, idles fine, not touching it.

I mean, what's the concern here? Higher fuel consumption?

FWIW my idle sits at around 800rpm or so as well. And yes, it runs fine, idles fine and there are no issues as far as I can tell. I don't quite see the problem.

[silviaz]

26 minutes ago, soviet_merlin said:

I mean, what's the concern here? Higher fuel consumption?

FWIW my idle sits at around 800rpm or so as well. And yes, it runs fine, idles fine and there are no issues as far as I can tell. I don't quite see the problem.

I know it's probably not going to cause any major engine issues. I just had a more generic concern that it's technically not running right (I guess this means the rpm is not sitting where it technically should be) Though the other thing is, it's that my steering wheel is shaking at 1,100 rpm at idle until it gets warm (seemed to happen after I tightened my alternator belt, will be testing the alternator soon).

Edited February 2 by silviaz

[joshuaho96]

53 minutes ago, soviet_merlin said:

I mean, what's the concern here? Higher fuel consumption?

FWIW my idle sits at around 800rpm or so as well. And yes, it runs fine, idles fine and there are no issues as far as I can tell. I don't quite see the problem.

For me at least the reason why it bothers me is because it's indicative of a deeper problem. And that will nag at me forever. Especially because I have tailpipe emissions testing + evap leak testing every 2 years.

[Dose Pipe Sutututu]

1 hour ago, soviet_merlin said:

I mean, what's the concern here? Higher fuel consumption?

Emissions, fuel consumption, heat, noise, etc. most likely.

[GTSBoy]

Yeah, when I dialled my idle down, given how much time I spent idling at the lights in traffic on my daily commute, the effect on overall fuel consumption was absolutely noticeable.

[silviaz]

3 hours ago, GTSBoy said:

Yeah, when I dialled my idle down, given how much time I spent idling at the lights in traffic on my daily commute, the effect on overall fuel consumption was absolutely noticeable.

Interesting. My tuner said after the tune that my fuel economy would be better but it is the exact same from what I could tell even though my car was running rich before lol. How much do km do you reckon you get on a full tank of petrol on your commute?

[Dose Pipe Sutututu]

34 minutes ago, silviaz said:

How much do km do you reckon you get on a full tank of petrol on your commute?

a better measure would be Litres per 100km, a full tank is a terrible UOM.

[GTSBoy]

10 hours ago, silviaz said:

How much do km do you reckon you get on a full tank of petrol on your commute?

The nature of my commute has changed. Way back then it was traffic lights all the way, for ~28km. It sucked. When they finally stitched the expressway together I could do a good 15+km of it at a steady 80-100 with no stopping. That alone has gotten me down to flat 10s. Prior to that it was mid-high 10s.

I can't remember the delta that I saw when I got the idle down. It was only ~150 rpm, because the idle speed was never terrible, but for the delta in consumption to be noticeable it would have had to have been at least 0.2-0.3 L/100km - which is not to be sneezed at when it comes for absolute free.

It's only about 50L per year, but that's ~$100. A few extra pizzas is always welcome.

Note that I have a record of every tank of fuel that has ever gone through my car except for a handful put in by someone else, like my mechanic. I can show you the difference between stock RB20 and tuned RB20, stock RB5Neo and tuned, winter and summer fuel blends, winter and summer fuel blends when the ambient temperature is not appropriate for the blend, working O2 sensor, blown O2 sensor, boosting f**k out of it and frightened to boost it because it is pinging, and so on. OK, I probably can't do all that now with 100% clarity - but at the time when any of those things were in event, you could see it in the records. There's 25+ years of simple tank after tank records, so you have to look for landmarks to work out approximately how old any single record is. What's really important is the meta data and that lives in my head.

[silviaz]

17 hours ago, Dose Pipe Sutututu said:

A high case of cbf.

Car runs, idles fine, not touching it.

 

One other question, is there a chance that changing the idle speed can lead you down a rabbit hole and is the reason the tuner didn't touch it? Reason I ask is because if that's the reason the tuner avoided it then I probably shouldn't be touching it lol.

[GTSBoy]

1 hour ago, silviaz said:

One other question, is there a chance that changing the idle speed can lead you down a rabbit hole and is the reason the tuner didn't touch it? Reason I ask is because if that's the reason the tuner avoided it then I probably shouldn't be touching it lol.

Not really, no. Anything you would do is easily reversible.

[Dose Pipe Sutututu]

8 hours ago, silviaz said:

One other question, is there a chance that changing the idle speed can lead you down a rabbit hole and is the reason the tuner didn't touch it? Reason I ask is because if that's the reason the tuner avoided it then I probably shouldn't be touching it lol.

If you don't touch the CAS, then you're fine.

[silviaz]

Hey all, I did a voltage test with the car (video attached) not running for 3 days. And here is some interesting stuff:

- Battery voltage is 12v (I had the key in the ON position)

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

- You will notice there was a sorta slow start but not as slow as it usually is.

- Idle surprisingly was better at just over 1,000rpm instead of 1,100 rpm.

- I turned on the A/C, radio and headlights in the video and the voltage remains the same

- I haven't cleaned the grounding wires on the chassis yet, that's next.

- Battery drops to 12.6v when I turn off the car and wait a bit

Seems like I might have a parasitic draw? I do have an immobiliser system which does drain the battery more of course but was wondering if there is anything else I should be looking at fixing? Does the ground wires on the chassis have anything to do with the low 12v? 

 

 

 

Edited Tuesday at 03:23 AM by silviaz

[MBS206]

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

[joshuaho96]

On 2/2/2025 at 2:54 PM, silviaz said:

One other question, is there a chance that changing the idle speed can lead you down a rabbit hole and is the reason the tuner didn't touch it? Reason I ask is because if that's the reason the tuner avoided it then I probably shouldn't be touching it lol.

Adjusting the idle screw is usually (emphasis on usually) just covering up deeper issues. Stuff like the cold start valve not closing properly. Throttle shaft seals on the way out. Coolant temp sensors getting out of spec. Coolant temp sensors especially can be a bear to diagnose because they can fail subtly. My dad just spent weeks chasing down his high idle. He cleaned the coolant temp sensor and everything but the resistance curve just drifts over time and if it's been 20+ years they also get super slow to respond as well. Has a massive effect on fuel economy as if it's off the ECU is going to run richer and command high idle for far longer than it should otherwise.