R34 GTT Idle / Deceleration Problem

[GoHashiriya]

Hi all,

Last week i took delivery of a 1999 ER34 GTT, RB25DET NEO (bone stock), the car has had an AT to MT conversion. I'm based in Japan and will start an introduction/build page once I organise the content. For now, I would love some input on a problem I'm experiencing with the car.

Upon the first drive I noticed the idle was high, approx. 1,200rpm. The fan would start at a high speed on cold starts and most troubling is that when coasting to a stop the revs would remain at around 2,000rpm until you stop dead where it would settle at 1,200. If I coast in gear it will continue to propel the vehicle forward.

After doing some research, It seemed it was worth cleaning out the Idle Air Control Valve, IACV (name check), adjusting the IACV screw and probing the TPS sensor to check for abnormalities. Today, I performed this task - the IACV was gunked-up a fair amount - and screwed the idle adjustment screw all the way in. The TPS reading was 0.42V at idle which I believe to be in spec.

Following this, the car now idles at 900rpm - which is fine by my standards, although not perfect - and does not hold at 2,000rpm on deceleration. However, there is now a brief surge at 1,200rpm on deceleration only, which occurs regardless of whether I'm in neutral or in gear.

I should also mention that the TCS and SLIP lamps came on during a test drive but have since disappeared.

I have ordered a 14pin consult port to USB cable and will get Nissandatascan once it arrives. Shipping time is probably a month as it's from China. So in the mean time, if anyone has any suggestions, it would be greaty appreciated.

[GTSBoy]

More cleaning. Spray some Subaru upper engine cleaner into it, then some WD40. Do that a few times. The IACV can be annoyingly slow to come good, and a single cleaning attempt seldom gets it there.

There is also a possibility that the speed signal is not working and that the neutral and clutch switches have not been wired up properly during the conversion. Any and all of these things can cause weird rev behaviour on decel transition to idle.

[GoHashiriya]

2 hours ago, GTSBoy said:

More cleaning. Spray some Subaru upper engine cleaner into it, then some WD40. Do that a few times. The IACV can be annoyingly slow to come good, and a single cleaning attempt seldom gets it there.

There is also a possibility that the speed signal is not working and that the neutral and clutch switches have not been wired up properly during the conversion. Any and all of these things can cause weird rev behaviour on decel transition to idle.

Thanks for the input. The latter makes a lot of sense; presumably this is something I can only determine with the appropriate software? 

I'll have another crack at cleaning the IACV over the coming days, there are some tight nooks and crannies in there that could probably have been cleaned better. The change in behaviour is the most puzzling thing to me as it really doesn't hint to what the cause may be.

Checking vacuum leaks is also something I'm yet to do but I was expecting different behaviour from a vacuum leak.    

[Dose Pipe Sutututu]

Are you running the an A/T ECU? if so then I suggest getting a M/T one in there OR just go straight to an aftermarket ECU.

[GoHashiriya]

9 hours ago, Dose Pipe Sutututu said:

Are you running the an A/T ECU? if so then I suggest getting a M/T one in there OR just go straight to an aftermarket ECU.

I'm not sure - is there an easy way of checking? I was under the impression the car wouldn't run properly (if at all) without an MT ECU. 

The car was swapped before purchase. Strangely, it was swapped with an R32 transmission. I know, I know, this transmission doesn't have a particularly good reputation for longevity with the increased torque.  

I currently don't have plans to switch the ECU until approximately a year from now when I start accumulating engine parts.

[Dose Pipe Sutututu]

Have a look at the part number, I have a feeling that erratic idling is because of an A/T ECU.

I've attached P/N I've found off the net, not 100% sure if they're accurate but worth a try.

[GoHashiriya]

8 hours ago, Dose Pipe Sutututu said:

Have a look at the part number, I have a feeling that erratic idling is because of an A/T ECU.

I've attached P/N I've found off the net, not 100% sure if they're accurate but worth a try.

 

 

 

Massive thanks for this - there is a difference in the second last digit between DET MT and AT variants. I will use this for reference and try to locate it on my ECU. 

Following your initial response I did a brief bit of research on the swap process and came back with information saying an ECU swap was not necessary, just that certain AT-specific ports became redundant afterwards. It is something I will need to look into further for sure. My initial thoughts upon purchase were that the swap has been done, so I can forget about it - rookie. 

I guess in the mean time I could also try unplugging the MAF and running it, just to tick it off. 

[GoHashiriya]

Hi all, a little update after driving this week:

The car will go cold when driving conditions are predominantly off throttle, e.g. on a downhill section when the engine is mostly on overrun. The water temp gauge will go from the 1/2 mark to 1/4 until the driving conditions normalise. The oil temp gauge also doesnt seem to ever get off the minimum mark (70'C) during very light driving - 20mins or more into the drive.

This situation is making me question the temp sensor or thermostat. If anyone has any information on whether these can also cause idle troubles, it would be a great help.

I haven't received the consult cable yet so am currently unable to troubleshoot this way.   

[GTSBoy]

Thermostat not closing is most likely culprit for running cold.

An engine will definitely drop temperature on overrun without fuel, but the thermostat should close and after that it should stop falling as rapidly.

[GoHashiriya]

24 minutes ago, GTSBoy said:

Thermostat not closing is most likely culprit for running cold.

An engine will definitely drop temperature on overrun without fuel, but the thermostat should close and after that it should stop falling as rapidly.

Thanks, I'll add a new thermostat to the to-do list. Can a faulty thermostat be linked to the other idle/hesitation issues? 

[GTSBoy]

52 minutes ago, GoHashiriya said:

Can a faulty thermostat be linked to the other idle/hesitation issues? 

Shouldn't. Not to the extent that you're talking.

[joz]

I think everything you said is normal. I have the same on my factory manual ER34.

[GoHashiriya]

On 1/7/2021 at 6:22 PM, joz said:

I think everything you said is normal. I have the same on my factory manual ER34.

Cheers for the response. If you're referring to the idle/deceleration issues, I'm certain it's not normal. I borrowed a factory manual ER34 before receiving mine and the characteristics were as a normal car should be - idle at 700ish, incrementally lower RPM from cold to hot, no surging/hanging on deceleration. This is unfortunate for me, I realise.

Pic of borrowed ER34 and mate's S15: 

[GoHashiriya]

Hi all,

My USB/consult cable finally came through and I just plugged it in (cold engine) to get a reading. First thing I noticed was the Neutral Switch is set to off when I was in neutral and the O2 sensor was fluctuating wildly, subsequently the AF ratio was switching between lean and rich.

Edit: upon a quick search, O2 sensor cycling is normal**

@  Dose Pipe Sutututu, the ECU is an AT one, part number: 23710-AA513. Before i try swapping this out, is it possible the neutral switch or any of the NDS readings below could be causing this? 

 

 

Edited January 17, 2021 by GoHashiriya
Grammar

[GTSBoy]

Neutral switch maybe. Just fix it.

The rest of the data? Nope. all normal.

[MoMnDadGTR]

i agree with gtsboy, fix the neutral switch. coolant system could probably use some love. if you do the thermostat make sure you put it in properly. ive learnt this the hard way on my rb26....little jig pin likes to be at 12 o clock ended up doing the job twice. 

[GoHashiriya]

14 hours ago, GTSBoy said:

Neutral switch maybe. Just fix it.

The rest of the data? Nope. all normal.

 

3 minutes ago, MoMnDadGTR said:

i agree with gtsboy, fix the neutral switch. coolant system could probably use some love. if you do the thermostat make sure you put it in properly. ive learnt this the hard way on my rb26....little jig pin likes to be at 12 o clock ended up doing the job twice. 

Thanks for the feedback both of you. The neutral switch will be up there on the agenda. Any pointers for assessing it's situation? Will I need the car on a lift, or is this accessible through the shifter opening in the centre console? Bear in mind the car has an R32 transmission.

Thermostat pointer noted - cheers. I have an oil leak coming from the oil cooler in the thermostat vicinity, so hopefully pulling both will make it a touch easier for installation. 

 

 

[GTSBoy]

Neutral switch is on the RHS of the gearbox towards the front. There are 2 switches. One for neutral, one for reverse. You can try shorting the wires together to see if the ECU sees neutral. Google for pictures showing which switch is which.

[MoMnDadGTR]

not being rude but if you haven't already printed out the service manual for your car I highly recommend that...for the r32 gtr its about a 600 page printer hit. may seem old school but it works and has great diagnostic steps throughout for solving issues like this.

[GoHashiriya]

On 1/19/2021 at 5:29 AM, MoMnDadGTR said:

not being rude but if you haven't already printed out the service manual for your car I highly recommend that...for the r32 gtr its about a 600 page printer hit. may seem old school but it works and has great diagnostic steps throughout for solving issues like this.

That's alright. I have got a copy already, albeit only the R34 one which presumably doesnt cover my 32 trans. Thanks for the reminder though as it did slip my mind.