R34 GTT idle problem

[Danowner]

Most likely one of the thousands of posts about idle problems with an RB engine. So, my r34 has been running like a dream. I've owned it for about 4 months, and never had a single problem. Put in a boost controller myself about 2 months ago, never had a problem. In the last week, my car has decided to drop to 500RPM when warm, and at a complete stop, and in the last day, it's done the same thing, but the idle was very rough and a bit up and down. Here's a video of my car idling, ignore the engine as for some reason on camera it comes out to be extremely loud, but IRL is a lot quieter for some reason. I just wanted you to focus on the exhaust pattern, as that's what I'm referring to when I say rough idle. This morning when I cold started it, it did the rough idle thing, dropped to 500RPM, and went rough, rough rough and then stalled for the first time ever, started it up 2 seconds later and was all good, started fine no worries. I took of the cam cover to check the timing belt, but it looks like it's in very good condition. No tears or anything. Here's the video: R34 idle Problems

 

I'm in need of some feedback if possible, just some recommendations on what I should look to fix, maybe if someone has experience the same problem I'm having. Cheers heaps guys!

[GTSBoy]

It's misfiring.  Could be recent change in fuel composition (end of winter mix, start of summer mix) depending on where you are.  Could be dirty plug(s).  Could be dirty AFM.

The video showed it idling at ~1000rpm.  I assume it was still warming up.  If it's settling to 500 rpm (where it should be aiming for 650rpm) then that could be because of the miss, or it could be because the IACV is clogged enough to stop it controlling.  The IACV incorporates a wax pellet cold start valve that gives you your cold engine high revs but it will close as the coolant warms and if the IACV can't control with the stepper motor then you can lose idle revs.  I had to clean mine recently because of this.  Was dropping to (nice) idle of 400rpm.  Not satisfactory for driving though, as it can and will stall.

[Danowner]

Cheers heaps GTS boy, i did actually experience misfiring about a week or 2, took out 1 of the coils looked fine (was late and had to get somewhere), so I just put it all back together after checking 1. I was driving to 80km/hr and was in 2nd at about 5k RPM, car made what I can describe as a 2step firing noise, then kept going. That happened twice but under the same circumstances, never had a problem since. I checked the consult port for errors, and got code 55 which is 'no malfunction', so that's all clear. Just bought some throttle body cleaner, will get to all the air control valves when I get home. Really appreciate the help, and will keep this thread updated just in case anyone else has the same problem

[Danowner]

Cheers heaps GTS boy, i did actually experience misfiring about a week or 2, took out 1 of the coils looked fine (was late and had to get somewhere), so I just put it all back together after checking 1. I was driving to 80km/hr and was in 2nd at about 5k RPM, car made what I can describe as a 2step firing noise, then kept going. That happened twice but under the same circumstances, never had a problem since. I checked the consult port for errors, and got code 55 which is 'no malfunction', so that's all clear. Just bought some throttle body cleaner, will get to all the air control valves when I get home. Really appreciate the help, and will keep this thread updated just in case anyone else has the same problem.

[Danowner]

Also, just driving my car now, I'm experiencing really strong stutter when I'm upshifting, feels like turbo lag but turbo is hitting boost fine on the stock gauge. I'd explain it as stuttering but it's more of a hesitation, I'm shifting at about 5k, and it takes a good second to actually tourqe up again, and keep powering, hence why it feels like turbo lag, but yeah hitting high PSI fine

[GTSBoy]

It's missing.  if it will miss at idle it will miss worse under load.

[Danowner]

Here's an update: so I've changed the spark plugs, used electric dialect on all coil packs and cleaned all of them. It must be just a faulty coil pack. I've also cleaned the AFM sensor with some contact cleaner. Literally no change in performance. This must narrow it down to be the coils. I'm looking to get some spitfire coil packs, might as well go all out as I'll be adding heavy mods soon.

[Danowner]

Update 1,000,000: I've put spitfire coils in, literally no difference. I am lost. I have no idea what this could be now.

[Billyboy369]

I know that it’s been two years, but did you ever find out the problem, I am having the same in my 1999 R34 RB25DE NEO, have replaced the coilpacks and harness and spark plugs, have checked my AFM, and no change have put some injector cleaner in and there was a slight improvement but it’s still idling low and rough 

[silviaz]

On 10/12/2018 at 5:56 PM, GTSBoy said:

It's misfiring.  Could be recent change in fuel composition (end of winter mix, start of summer mix) depending on where you are.  Could be dirty plug(s).  Could be dirty AFM.

The video showed it idling at ~1000rpm.  I assume it was still warming up.  If it's settling to 500 rpm (where it should be aiming for 650rpm) then that could be because of the miss, or it could be because the IACV is clogged enough to stop it controlling.  The IACV incorporates a wax pellet cold start valve that gives you your cold engine high revs but it will close as the coolant warms and if the IACV can't control with the stepper motor then you can lose idle revs.  I had to clean mine recently because of this.  Was dropping to (nice) idle of 400rpm.  Not satisfactory for driving though, as it can and will stall.

Is the 650rpm idle on the rb25det neo for stock cars only? I've never had my car before and after tuning it to idle at 650rpm when cold. Always idle's cold around 1100rpm, and then drops to about 900-950rpm. I've heard the r33 gtst's idle there. 

Edited February 1 by silviaz

[GTSBoy]

Unless you have big cams, there is no reason for an RB to idle at any more than the stock 650. No, it is not 850, 950, or anything else. It is 650.

In fact, it might even be 550. I just opened an arbitrary stock Neo file in Nistune, and this is what I see

[tsuokun]

I would like to add that at least in my car, the RPM gauge shows around 200RPM above of what I can see at nistune.

[silviaz]

2 hours ago, GTSBoy said:

Unless you have big cams, there is no reason for an RB to idle at any more than the stock 650. No, it is not 850, 950, or anything else. It is 650.

In fact, it might even be 550. I just opened an arbitrary stock Neo file in Nistune, and this is what I see

Oh ok, so looks I should be resolving this? I was thinking of cleaning the iacv, and maf for a start and checking for any loose hoses. Already did a boost leak/smoke test and was all in the clear.

I'm suprised the tuner didn't say anything.

[joshuaho96]

4 hours ago, silviaz said:

Oh ok, so looks I should be resolving this? I was thinking of cleaning the iacv, and maf for a start and checking for any loose hoses. Already did a boost leak/smoke test and was all in the clear.

I'm suprised the tuner didn't say anything.

If it's been tuned idle rpm can be changed.

[silviaz]

4 hours ago, joshuaho96 said:

If it's been tuned idle rpm can be changed.

Yep. Saw that on the image above but, wonder if it makes more sense to clean out the iacv because let's say in theory mine is dirty and if I clean it the rpm will drop. If I first go to my tuner to drop the rpm and then go to clean my iacv won't it drop further or is the rpm a fixed number?

[Dose Pipe Sutututu]

What ECU is on your car @silviaz?

You can just change the idle target table yourself and the IACV duty cycle. Noting that if you play around with the screw you'll also need to revisit the idle base duty table as you will end up offsetting the lot.

Another reason why DBW is superior, there's less mucking about.

[silviaz]

10 minutes ago, Dose Pipe Sutututu said:

What ECU is on your car @silviaz?

You can just change the idle target table yourself and the IACV duty cycle. Noting that if you play around with the screw you'll also need to revisit the idle base duty table as you will end up offsetting the lot.

Another reason why DBW is superior, there's less mucking about.

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

[joshuaho96]

59 minutes ago, silviaz said:

Yep. Saw that on the image above but, wonder if it makes more sense to clean out the iacv because let's say in theory mine is dirty and if I clean it the rpm will drop. If I first go to my tuner to drop the rpm and then go to clean my iacv won't it drop further or is the rpm a fixed number?

The RPM is just a target, the ECU will adjust things to try and hit that target but it's by no means guaranteed. If the IACV duty cycle is 0 or something like that and it's actually closing up fully then the idle is as low as it can physically go without reducing ignition timing. The problem can be something like the cold start valve in the IACV not closing fully, worn throttle shaft seals, torn rubber diaphragm in the brake booster allowing unmetered air, etc. 

[silviaz]

10 minutes ago, joshuaho96 said:

The RPM is just a target, the ECU will adjust things to try and hit that target but it's by no means guaranteed. If the IACV duty cycle is 0 or something like that and it's actually closing up fully then the idle is as low as it can physically go without reducing ignition timing. The problem can be something like the cold start valve in the IACV not closing fully, worn throttle shaft seals, torn rubber diaphragm in the brake booster allowing unmetered air, etc. 

Ah right that makes sense.

[GTSBoy]

Yeah, you want the IACV to be running at around 30 "units", variously called "steps" or "duty cycle" depending on the person. That gives it room to go lower if need be and higher ditto.