I have read many descriptions of cold start/idle problems on this site and elsewhere, but none seem to match the issue I'm having. My issue is not just for a minute or so like others seem to be. I describe symptoms in gory detail below. I wonder if it is something that has plagued anyone else's G37, but the closest I saw was on a Bimmer forum and it was a dead-end, info-wise, as is so often the case.

My car is a 2009 G37 Sedan (Journey with S package) with 79K miles. Original plugs/wires/injectors. It has had any work done on the engine, just oil changes and air filters.

Problem: When the outside temperature is chilly - under 60F, it runs like a plug wire is disconnected for about 15 minutes. Power is down, throttle response is laggy, and I have to give it more throttle than normal to get going. At 4K RPM and above, there is a loud droning noise in the cabin and a lot of vibration from the drivetrain, felt through the pedal and steering wheel mainly. It sounds and runs like a lawnmower.

Even with the coolant temp gauge at normal range, i.e warmed up, it still runs badly until it's driven for a full 15 minutes. Once it smooths out it runs like new the rest of the day. During morning commute the day is warming up so the ambient air temp is where I'm focusing. The next morning, if cold, it happens again. If it's a warm morning though, it's smooth and quiet through the rev range.

I'm not sure when the problem started as my wife was driving it daily (many short trips), and she didn't notice it, but boy, I sure do.

I had an independent shop's master technician (so they said) who spent 15 years at Infiniti/Nissan dealer look at it. He could not figure it out and went down some false leads, IMO, looking at the symptoms, not the cause. He said it could be an imbalanced driveshaft. He noticed the vibrations, but that diagnosis makes no sense to me, why would a driveshaft problem affect the performance of the motor and not happen with a 10-degree difference in temperature outside?

I cleaned MAF and Throttle bodies - they were pretty grungy. After this the CEL came on, I had codes pulled and it said 'high idle'. The light went out after about an hour of driving and it hasn't come back on. Prior to that, the codes don't indicate any misfires, and the check engine light had never come on. There's no change in the behavior. I also bled the cooling system, thinking the coolant temperature sensor might be involved - but again this doesn't jibe with the symptoms related to the outside air temperature that I have subsequently been narrowing down on.

For anyone who read this far and has an idea, I welcome the thoughts.

 

Only cold not wet? Seems like there is some valve / actuator /sensor that is sticking in cooler weather, but is not very close to the engine, and it takes 15 minutes to warm up enough to operate. Would you describe that as accurate?

Rough idle / running could be vacuum leak, bad electronics. Or even the VVT not behaving correctly. Though the latter would almost definitely throw a code.

My initial guess was something in the evap system. That's a complete WAG.

Good luck, let us know what you find.

 

just because your temp gauge shows normal range does not mean your engine is warmed up fully and the pcm running at closed loop. since you stated you drove it for 15 minutes that should be enough to have the t-stat open and vehicle now running in closed loop parameters. as for the the cold temp causing the symptoms do you have a scan tool to check the air mass with? its possible one of the intake air temp may be faulty in the air mass and providing inaccurate feedback to the pcm creating driveability issues that you may be experiencing. highly unlikely for it to be a vacuum leak since that would be a constant problem.

 

Your issue is a little unusual and will require special tools to troubleshoot. Here are my thoughts:

Have a look at the mode $06 misfire counters to see if one cylinder is higher than the others. That might give you a cylinder to focus on.
If you are looking for a good app to gather that data, OBD Fusion (with a cheap OBD scanner) does a good job interpreting the mode $06 data. Torque Pro does not.

Also, using OBD Fusion to look at your fuel trims. Add the short term to the long term to get the total fuel trim. If the total fuel trim if > 15%, there might be a leak in the intake or PCV system.

Pull out all the plugs and have a look at their condition.
In some cases, the spark plug tube can get filled with engine oil and that may cause that cylinder to misfire.

My next step would be to use a scope and look at the ignition coil current.
If you scope the common ignition coil ground, you will be able to see all 6 coils in operation and easily determine if a coil is not operating properly.
(have a look at this: )

I would also check fuel pressure during a cold start. It should be around 51 PSI at idle.
This does require a "fuel tap" since there is no easy way to "tap" into a return-less fuel system.

If you don't have the time or required tools, you could always ask a shop for these tests.
The good news is that the problem is always there when cold, so it shouldn't be too difficult to determine the cause.

Good luck!

 

Thanks to all your replies, I'll consolidate my reply.
Rooster Tail - just cold is enough, it doesn't need to be a rainy day. I don't think I've had more than one of those in the month or so I've been noticing it (in LA area).
crookncastle - I don't have any of these special tools, I was hoping the tech had what's needed. They said they didn't find any 'old misfires' so I assume they had a way to check.
SonicVQ - I don't even have a socket wrench that'll fit down the hole at this point, so I'll start by getting one and pull plugs. Not sure which reader they used to check misfires, can ask if I decide to try them again or someone else, but I've been burned 2x with no result so far.

 

Have you changed trans and diff fluid yet

 

I had both changed along with coolant and brake fluid flush about a month ago the first time I brought it in for diagnosis. No difference. It's noticeable even at idle in park when revving it, so it seems to me to be isolated to the motor. I can just about guarantee a carbureted vehicle with old fashioned points/coil ignition would never have this problem, as I've grown up and old on them and have never heard of such a specific situational problem. So I'm thinking it is related to the ignition/computer/fuel injection or some combination of those.

 

After all this time, I'm resurrecting this thread. I no longer own the car - my ex does . My son is trying to help get it fixed. It's awful - under about 65F, it's a box of rocks for quite a long time, until fully warmed up (10 minutes or more) I want to help him out.

I see that others have had similar problems - this one seems exactly like it, and another reply was "mine too". But no answers.

What I'm trying to find out is this: Has anyone had this problem - not close to it, but exactly, and had it fixed? I am not going to be able to diagnose it, buy special tools, etc. I brought it to the dealer 1x and to two 'Infiniti experts', which wasted money, and didn't fix a thing.

I recently helped replace the fuel pulsation damper as it was leaking (right above the exhaust!), and I thought maybe this was it - I read threads that said low fuel pressure could be the issue. Nope. The car has 100K miles, and runs fine on warm days or when it's warmed up completely on cold days.

Plugs? I've never heard of plugs causing something like this. Coils? They usually break down with heat. I cleaned the throttle body and MAF. The transmission fluid and coolant was changed at 80K, made no difference.

I thought of calling yet another specialist and asking the same question, but they don't like what they consider 'fishing' questions. Bring it in and spend $$$, maybe they'll find it - nope.

 

While I am not one to "bump" threads, thought necessary in this case as, for the first time in my G's 18-year life, this specific issue has arisen. Same identical symptoms as in post #1 above and also in this post.

The patient: 2008 Coupe, ≈132K miles, No engine mods save for R2C Intakes and Fast Intentions RHFC's with IPL catback. The symptoms:

Yesterday, by my NY standards it was chilly (<30s). By Eastern NC standards, brutally cold. Had to run errands, car started fine but sounded different. These cars are notoriously loud at cold/ fast idle so I thought nothing of it. As I always let my cars run a few minutes to "warm up" there was plenty of time for the idle to settle down. Rock solid at 650ish. Put it in gear and I hear this "rumble" sound. There is no discernible/ physical vibration just a grumbling/ rumbling "sound" that varies with RPMs. I have a super long driveway so the sound was obvious. Go to get on the highway and, while the car moves, it is not as "peppy" as it usually is- I wouldn't say hesitant or sluggish- but not crisp and linear as per the norm. After about 30min.- by the time I arrived at stop #1- the sound had abated. Upon restart all was fine- peppy, smooth, and quiet. It is not the 5AT as the "rumble" is heard even when I put it in neutral. and I do not suspect anything VANOS VVEL-related.

It was a hassle but I plugged in the OBD dongle and fired up OBDFusion on the iPad. No codes, no "misfires", everything "green" according to the OBDFusion Diagnostic Report. Nothing out of the ordinary but at this time the engine was fully warmed up and running smoother than silk.

Flash forward to this morning, 30 degrees outside, starts up fine but that rumble is back. Was too early to fiddle with it but will in the coming days.

To note, I do suspect a exhaust leak at Bank 1 FI RHFC (maybe both)- no specific reason just a hunch based on sound and smell and that will be checked/ addressed when the car gets it's annual spring underbody checkup. I am not crawling on the ground in 20+ degree weather. All fluids and belt recently changed- tensioner and all accessory/ idler pulleys fine. Spark plugs will be due in another 20k miles or so (every 75k miles). TB cleaning TBD during annual spring cleaning maintenance. Same petrol station/ brand (BP and Shell) and 93 octane that I've been using for decades. Only puzzling issue that there are zero codes and the exhaust smell.

I will have to repeat the logging session (if the damn iPad cooperates) and go from there. @SonicVQ I know you are not active as much on here as in the past, but have you any suggestions on what specific items/ pids to log aside from STFT, LTFT, and lambda?

Open to all suggestions and TIA...

 

Issue persists. I "believe" the issue is with bank 2- at least that is where I perceive the "grumble" to be emanating from. After 20min. of normal driving the sound just "disappears." Hard to explain, but there are zero codes and the OBDFusion "Diagnostic Report" is all green. I tried taking a recording of the sound but that flopped.

I am attaching 3 logs (csv) from yesterday's trips. At the risk of sounding presumptuous, if anyone has any spare time and can give them a quick looksee to find out if anything sticks out of the ordinary. I "believe" I have OBDFusion setup correctly though, even with the "Enhanced Nissan/Infiniti" add-on things I question the reliability of some readings and some just will not work at all- maybe because mine is a 2008 and, apparently, there are limitations therein?

I do suspect either upstream (AF (wideband)) and/or downstream (O2 (narrowband)) sensors as they are original to the car (17/18-years) and ≈132K miles. Plus the exhaust smell seems rather "rich" than in past. Still, no codes though... and where my mileage has historically been 23-25mpg it's now 19-20mpg (pen and paper, not idiot computer).

Open to suggestions/ things to check/ other items to log/ etc. TIA to all.

 

Had to go to a farewell party for a close friend last night and, luckily, traffic was relatively "light" thanks to the impending "Snowmageddon" nonsense. Anyway, I was finally was able to make a halfa** recording of the rumble. It is hard to hear but it is most pronounced at gear changes. And, again, is not the 5AT as the rumble exists whether in gear or P/N.

Also attaching the OBDFusion report from last night (well, this AM)... ignore the BCM codes- I could care less about the damn TPMS sensors and I intentionally have the ESCL disabled. None of those would have any causation to the noise which goes away after 15-20min. or so.