Rb25 into r31/wont idle

[Liam2421]

Hey guys looking for abit of guidance, I have put a 25det into my r31 and am having trouble getting it to idle it will rev fine and not miss but on idle it runs like abit of a dog and stalls, I checked the tps voltage and it was 5.10 with car switched off I’m unsure if that is in the perimeters? other then tps could the iacv be the cause or potentially vvt ? I realise it could be a range of things but have to start somewhere, cheers 

Edited September 14, 2024 by Liam2421
Grammar correction

[GTSBoy]

At idle the TPS should show about 0.45V.

Yes, it could be the IACV and/or AAC. Got tbe clean and working to do what they're supposed to do.

Will not be VCT unless perhaps it is stuck on. Even then, it should idle.

[Liam2421]

On 15/9/2024 at 5:00 PM, GTSBoy said:

At idle the TPS should show about 0.45V.

Yes, it could be the IACV and/or AAC. Got tbe clean and working to do what they're supposed to do.

Will not be VCT unless perhaps it is stuck on. Even then, it should idle.

Un able to check it at idle as it won’t idle for me long enough to try, best I’m able to do is with ignition on engine off and no matter where I turn the tps the voltage doesn’t change from 5.10, if I unplug afm it will idle longer but won’t turn off with ignition, have since swapped afm to no real change 

[GTSBoy]

6 hours ago, Liam2421 said:

Un able to check it at idle as it won’t idle for me long enough to try,

Doesn't need to be idling. Just needs to be throttle closed with ignition on. Same same as idle from the ECU's point of view.

6 hours ago, Liam2421 said:

best I’m able to do is with ignition on engine off and no matter where I turn the tps the voltage doesn’t change from 5.10

See, this is useful info, because this...

On 9/14/2024 at 9:58 AM, Liam2421 said:

tps voltage and it was 5.10 with car switched off

is not.

You should be able to sweep the throttle from closed to open and see it run from ~0.45V to whatever it maxes out at (which is not 5.1V, by the way - should be 4.something).

[TurboTapin]

7 hours ago, Liam2421 said:

if I unplug afm it will idle longer but won’t turn off with ignition

Your engine won't shut off with ignition if your MAF is unplugged? I want to confirm I'm reading that right. 

[Liam2421]

19 hours ago, TurboTapin said:

Your engine won't shut off with ignition if your MAF is unplugged? I want to confirm I'm reading that right. 

Yes it will continue to idle until eventually stalling between 10-20 seconds, still continues to idle even once  I hit the battery isolater or disconnect battery 

[Liam2421]

21 hours ago, GTSBoy said:

Doesn't need to be idling. Just needs to be throttle closed with ignition on. Same same as idle from the ECU's point of view.

See, this is useful info, because this...

is not.

You should be able to sweep the throttle from closed to open and see it run from ~0.45V to whatever it maxes out at (which is not 5.1V, by the way - should be 4.something).

Thanks for clearing that up, I see you comment on most posts it’s very helpful for less mechanically inclined people like myself so cheers, 

could you recommend other things to check ? All I have done to this motor since seeing it run fine in another car (completely stock)  is install a Freddy plenum and a 3076 on a top mount , replaced plugs and have split fires on the way currently 

[TurboTapin]

5 hours ago, Liam2421 said:

Yes it will continue to idle until eventually stalling between 10-20 seconds, still continues to idle even once  I hit the battery isolater or disconnect battery 

What in the absolute mind f**k. Generally speaking, you cannot diesel a petrol engine without sparkplugs which you don't have since you're disconnecting battery.... Something is very fishy here. 

[MBS206]

20 hours ago, TurboTapin said:

What in the absolute mind f**k. Generally speaking, you cannot diesel a petrol engine without sparkplugs which you don't have since you're disconnecting battery.... Something is very fishy here. 

You don't lose spark if your battery isolator isn't wired correctly and the ECU still has power from the alternator.

 

Car has an epic wiring problem. Sounds like power connected really really badly in places. Possibly a power pin on a ground pin for the ECU, and constant power in locations that should be switched ignition.

 

It needs someone good at diagnosing electrical, a good multimeter, and someone with the wiring diagrams to match the engine loom that has been put into the car, and wiring diagrams for the body side of things from the car.

[TurboTapin]

7 hours ago, MBS206 said:

You don't lose spark if your battery isolator isn't wired correctly and the ECU still has power from the alternator.

 

Car has an epic wiring problem. Sounds like power connected really really badly in places. Possibly a power pin on a ground pin for the ECU, and constant power in locations that should be switched ignition.

 

It needs someone good at diagnosing electrical, a good multimeter, and someone with the wiring diagrams to match the engine loom that has been put into the car, and wiring diagrams for the body side of things from the car.

Agreed. Thing has to be running absolutely pig rich as well. I would worry a lot less about your idle and start going through all your electrical before the car burns down.