Strange idle problem with GTM SC Stage 1
 

I sent an email to my tuner and Sam at GTM, but I wanted to see what the other FI people thought about this idle problem. I have had this problem since the SC kit was installed several months ago. Other than this idle problem, the kit has been fantastic.

Everything pointed to slight exhaust leaks I had with some test pipes. So I put the stock cats back on using all new OEM hardware including inlet/outlet gaskets. Going back to the stock parts fixed the daily SES lights, so I am 100% sure there is no exhaust leak now.

However, I still have an erratic idle. This is video of the problem. It happens at least once a day. What do you guys think might be causing this? You have to watch the entire video, but the car tries to die at about 40 seconds.

EDIT
The problem usually happens after exiting the highway and stopping at a traffic light for example. I was just able to get the video on a restart of the car. It only happens when the car is well warmed up.

Weird. I don't have that problem. What spark plugs are you using?

If I remember correctly, they pulled the OEM plugs to verify they would work OK. I am almost positive they just changed the gap on the original plugs.

I haven't had that problem ...

Dont count on me on this one as i do not know for a fact if spark plugs will adversly affect the idling. Just a suggestion, before when I had the STILLEN sc I was running stock spark plugs also and had major idling issues, wayyyyy worse than what you're experiencing.

GTM did installed some HKS spark plugs on my car when I switched kits. Now I don't have any idling issues at all!

It could also need to have the ECU relearn the idle... I had this problem on my G37 and that took care of it.

Im not sure if that is the same problem you are having... mine would die while coasting... scary when Power steering didnt work anymore!

Mike

Is the AC compressor kicking on?

The erratic idle is independent of the AC. It happens with the AC on or off. It was off during the video.

Thanks for the responses. I am waiting to hear back from Sam and Kenny, but I am leaning towards changing the plugs and trying the ECU learning.

If you watch the video close from start to finish, you see the idle bounce around 50-75 maybe 100 RPM. It feels like a slight knock which I hope are the spark plugs. Then at around 40-43 seconds in the video when it dramatically dips, the car shudders and usually the idle shoots to 750 and stays there. It is really odd but it happens at least once everyday. It is hard to reproduce though. I cannot make it do it.

Bullitt
Mine has never completely died. It comes close and only at idle for 30-40 seconds like at a stop light. It does not happen when rolling luckily.

weiboy718
Do you know the part number for the HKS plugs?

is the car not supposed to drop to 500? my Gtm stage 2 occasionally dips to 500 at a red light and shudder slightly as if its gonna "stall" but always kicks back up. Seb at Specialty z says its normal.

Vapor lock?

I'll get you the part number tonight or better yet you can call Sam directly. Pretty sure he's got all the info you'll need and what you need to do.

These are the spark plugs GTM Motorsports*::*IGNITION SYSTEM*::*HKS M-Series Super Fire Racing Spark Plugs (Heat Range 8)

i know you gotta pay to play but damn!!!! $30 a pop. ouch!

My old M3 would do this too after I got it tuned. Never died, but sometimes felt like it was going to.

watching outcome for future knowledge :)

Agreed, Im contimplating a GTM stage 1 supercharger kit.

I may be wrong in this case of info but from the research I did when i was going to buy these plugs, the stock plugs in our car use the same ones as a GTR which are already heat range 8. Both part numbers are the same for the plugs if you were to order them from nissan. This i did call a dealership also and confirm, so it is safe to say I do not think the heat range of your plugs are the problem.

Mine will also stumble at idle from time to time and only when hot. I have never worried about it much.

Running the factory plugs as my plugs got to the house after I had already gotten the intake back together. Was more of a pain than I wanted to endure to take things off to get at the plugs in the middle of the SC install.

true statement about the stock plugs :tup: they are teh coldest we can use at the moment on these cars and are made by bosch. No reason to really change them out for I high price brand such as HKS.

EDIT: I found out a couple months ago when I was looking for a colder plug and contacted summit racing

part # from GTM
50003-M40HL HKS Sparkplug8HR

you should def ask a expert before taking the plunge though.

I doubt it's the plugs. Only if you had misfire codes coming up.

It's probably either reading a poorly tuned load cell at idle, an intermittent vac leak that causes a sudden misread, or something screwy where the belt is slipping and the idle revs up to catch the stumble. I guess it could also be something wonky with the MAF temp sensor readings too.

Can you data log when this happens?

Mine will do this when it is hot/warmed up.

Now I am wondering if it is normal because a few other people have the idle drop when the car is at operating temperature.

After going back to the stock cats (over 2k miles) I am throwing no codes and the stock plugs are in the right heat range. This makes me reconsider changing plugs.

I forgot my laptop today, but I will try and data log it tomorrow.

Thanks for the help.

Just a short update

Sam gave me a shout on the phone and I do not think this is a big deal. I am going to check some things and will update here.

Three things to check for this minor issue.

Spark Plugs
I cannot remember 100% what the shop said about my plugs during the install. I know they pulled them to verify the heat range and I used the original plugs. After talking with Sam, I doubt they changed the gap, but I am going to pull them to make sure. I may also go one step colder with new plugs.

ECU Correction
The ECU maybe be overreaching. I am going to get some readings and data logs and see the correction factor during various driving conditions.

Idle Learning
This is the 3rd step after checking the 2 above.

For those of you on the fence about the GTM kit, I suggest you take the plunge. I have been more than happy with the results. It is hard to wipe that S_ _T eating grin off my face lately. I was more or less curious why the car idled funny and this is not a serious problem. It is my DD and I notice things.

That is when I noticed it, daily driving my car is the only time it occurs.
If I drive it on a Saturday, no traffic around town it is fine, but sitting in traffic or hot days is when mine will drop then bounce up.

This exactly.

Just got off the phone with my tuner, and he assured me my spark plugs were just pulled as a verification process. There was no adjustment to the gap.

I am going to do what Sam suggested with checking the ECU correction, but I bet the idle needs to be relearned. Mike @ Bullitt@UAMotorsports suggested this earlier in the thread. The board is a great source of information.

I dont think your understanding what I said earlier. Not trying to be a *** when I said that, just want you to have all the knowledge so please understand that. There is no one step colder plugs for our car. The stock plugs in your car are the same ones the GTR use. The heat range on the stock plugs is heat range 8. There is no colder plug then that on the market currently. Just don't want you to go buy heat range 8 plugs thinking your getting colder ones when in fact your putting the same ones in your car that you have currently and end up wasting money. Like I said earlier your spark plugs are not the problem. Like Jordo said you would have a CEL if it was.

No worries and thanks for the information. Going one step colder was something Sam suggested on the phone today.

I am actually not doing anything with my plugs. After having a chat with Kenny (my tuner) nothing was done with my stock plugs. The installer pulled them to check that they were the correct plugs, no harm in that. It was just a verification process which is a good practice. I thought I recalled something about the gap being changed, but I was wrong. That was my ignorance.

I appreciate the information and understand where you are coming from.

Maybe it was my fault for being it up haha.

Frank just to clarify couple things Here

The GTR spark plugs are not the same as the 370Z plugs, also HkS does offer one step or two step colder spark plugs.

Sam

While on the topic of HKS spark plugs, what's the recommended replacement interval? Every 20k miles? 30k miles? 50k miles?

With a good running car( Good Tune ) 60 to 100 k

Sam

Hmm weird. considering the fact on HKS website they show the heat range 8 plugs having the same exact part number as the one for the GTR. Also when I went to the dealership I was thinking of getting the GTR plugs, thinking they would be a little cooler and after pulling up the info he said they were already the same exact heat range already the two plugs and using the referance chart it would be equal to a heat range of 8. I just checked NGK website and they are also showing the same part number on the application chart with the OE sign.
Hmm guess I am wrong, just weird there is someone else on here who said he got the same exact information.

I spoke to HKS a while back. They told me that their spark plugs are 1 degree colder than listed.

interesting

Mine does this as well everyone once inawhile. I never paid any heed to it. It only did this at idle and after a good run. My kit is running great. Best purchase I ever made

bit of a thread revival - could someone post up pics or a description of where the pcv vent FRESH air hoses have been routed?
ie. NOT the two hoses which go into the front of the intake manifold.
or a link to the install instructions?

cheers mate, i've just had a look at it.
i'm not a professional mechanic but i can share what i did to my Stillen G3 intake to resolve the same problem you're experiencing.

Page references are based on the labels at the bottom of each page.

Apologies for the use of two units of measurements - i'm from Australia where using both is acceptable depending on the context.

The stock breather system has these features:
RHS - 13mm restrictor orifice is in the junction where the breather hose barb pokes into the accordion pipe.
LHS (USDM driver side) - no restrictor. It is 16mm throughout. 16mm is approximately 5/8".

Page 61: The breather hose has a 5/8" inner diameter. Therefore the outer diameter of the barb it connects to on the supercharger intake is approximately 5/8". The barb's ID would have to be smaller (by quite a bit in this case, as it appears to have quite thick walls).

No issue quite at this point, as it seems to match the OEM setup in terms of hose inner diameter and the inner diameter of the barb fittings.

Page 70: Describes how a tee is used to join both cylinder banks' breathers together, drawing fresh air from the single 5/8" ID hose.

Because of this, the intake of fresh air is restricted by half at this point, and i reckon this is the cause of the sagging idle/stuttering issues you guys have experienced.

On my Stillen CAI, i cut off the LHS breather barb which has an ID of 12.5mm. Welded on a barb with ID of 15.5mm and my idle is about as good as it was with the stock intake now. RHS is left as Stillen made it.

As a simple test, i'd suggest disconnecting the tee and using a straight joiner for the RHS bank. ie. isolate the LHS breather.
For the LHS breather, clamp on a suitable small pod filter. Go for a drive and see what happens. Then try the idle relearn procedure if theres no difference (can be done without scan tools).

Ideally the breathers should draw from after the MAF sensors as the ccv system does recycle the crankcase fumes and burns it up. The fresh air drawn in to replace the fumes should be metered to ensure correct AFRs. But for a quick test it shouldnt hurt. The GTM setup draws from a suitable location but i reckon if you run another 5/8" hose to a new extra barb, it should unchoke it :)