BoomerSpeed01

So ever since I got my sedan last summer, it has never done the typical VQ high idle upon startup. When I had my coupe I know it went about 1500rpm and that was very typical throughout the VQ equipped G's. This sedan does not do that...
Is there something wrong? Is this an abnormal oddity, but harmless? Hopefully there's nothing wrong. Now that I've had a modified exhaust for a while, I'm really starting to miss that high idle upon cold starts lol

Noogie Lamont

The issue has nothing to do with your exhaust at all.

I have found that the RPM range on cold or warm startups depends on what oil brand you use.

For example if I use Mobil 1 upon a startup(cold or hot) the engine will start up at around 12-1300 RPM's and within 30 seconds go back down to 800 or so.

If I use Castrol, Pennzoil UP, Or Redline the car hovers around that 11-1300 RPM mark for a Min or so and then gradually goes down but it takes ten mins or so to get the effect that the Mobil 1 gives in under a min.

What oil are you using? Your issue seems very normal especially for Mobil 1.

From my experience with this engine you have nothing wrong.

On the other hand my Z06 is super loud with the Borla Exhaust on a cold startup. Not as loud as some of you guys with an ARK but still loud.

BoomerSpeed01

I am fully aware that this is not caused by the exhaust... I was just saying that I miss the high idle on cold starts since I got a custom exhaust and in my opinion the cold starts sound amazing with the right exhaust setup.

Not so sure that your oil theory is what's going on here. I had a 2010 G coupe before my current sedan, and it did the high idle on cold starts every time, and I'm still using the exact same oil I used with the coupe. Pennzoil 5W30 High Milage Full Synthetic.

Any other thoughts?

Noogie Lamont

I read your posting wrong.

To your question. Yes the 1500 RPM high idol is just a tick abnormal.

I have a Stillen exhaust with Berk HFC's and Gen 3 intakes on my sedan and I have never gone over that 1300 mark on a cold startup and thats on a 10 degree day left out all night. Did your Coupe stay at that 1500 range or was it high for a min or so and then went gradually down as the engine heated up? Was the Coupe a manual or auto? All of my manual cars seemed to always idol a bit higher then my auto cars.

And the oil is not an issue. If you changed it the only thing it would do is make the RPM's go down faster.

BoomerSpeed01

Both coupe and sedan were/are auto. I don't remember exactly what the RPM was at on the coupe on cold starts and yes it went down once the engine had been running for a minute, obviously longer if very cold and shorter if warmer outside.

Once at running temp both cars would idle around 500-700rpm. On cold starts my sedan is right around 1000rpm, and I'm pretty sure my coupe was right around the 1300rpm, give or take.

Also to specify, I WANT my sedan to idle high on cold starts. That is the norm from what I've seen for VQ's and I love the way it sounds. I'm just trying to figure out why my sedan doesn't do that.

Noogie Lamont

My Sedan does the same as your Coupe did on very cold mornings. Right at about 1300 RPM for a few mins and then steps down as the engine gets warmer.

It's really not possible to extend the idol timewise past what the car is doing already. Everything as you know is computer controlled.

When you say cold start that could mean any tempature. I do not have the high idol in anything above about forty degrees.

I did notice however the car did not have the higher idol upon cold startup when the stock intake was in the car. It really only started when the aftermarket intakes were put on.

I am just drawing straws here but what was different mod wise between your Coupe and your sedan(as it sits now). I'm running a 13x BTW.

BoomerSpeed01

Mods are exactly the same (almost). Coupe had a muffler delete with two 18" resonators in its place, rest of the car was bone stock. Sedan is bone stock other than the custom Y-Back exhaust. Both resonators and mufflers were removed with two 18" resonators placed in the stock resonator location and 2.5" pipe the rest of the way back. Neither car had aftermarket intakes or anything like that.

I'm almost starting to think it could be the spark plugs. My car has some hesitation under 3-4k sometimes and at least two people now have stated that after changing plugs and cleaning throttlebodies, that the hesitation is gone. I wonder if the two are connected.

SonicVQ

The idle speed at a "cold" start is based mostly (90%+) on engine coolant temp.
Depending on where you live the overnight temperature can vary, so the cold start idle will also vary.

I have seen dirty throttle bodies that resulted in a lower cold start idle.
If you think that applies to you, clean them, then doe the intake idle volume air learning and everything will be back to normal.
PLUS you might enjoy the sharper throttle response.

BoomerSpeed01

I hear you 100%. Only thing is the throttle bodies were one of the first things I looked at, because I know they can cause issues like this. I couldn't even see any carbon buildup anywhere. Surprisingly clean.
That's why I think it could be the plugs. You did mention some sort of MAF idle learning... Is that one of those things you just do a sequence of actions and it reprograms that for you?

SonicVQ

A visual inspection for carbon build up on a throttle body is not very meaningful.
The outer edge of the throttle plate is what gives it the "fine" air control.

If you G37 has more than about 30,000 miles since the last throttle body cleaning, there is some carbon build up on that edge.

Incase you haven't done it before, here is one of the better videos:

After that, there are 3 different steps that should be done get get the ECU to re-learn the new airflow characteristics of the freshly cleaned throttle bodies:

If you have an Android device and a bluetooth scanner, you can use a free app to do the last (and most difficult) step. The "Intake air volume learning"

It is very unlikely that your spark plugs would cause a lower idle, generally you would have a misfire declared before a low idle and a flashing check engine light.

BoomerSpeed01

Ugh, I have an Iphone and a WIFI/Bluetooth scanner. I doubt anything on the app store will allow me to do that for free.

SonicVQ

You can still do it using a stop watch as shown in the second video.

Noogie Lamont

I really don't think changing the plugs or cleaning the Tbs or MAFs are going to help. I have done those and it makes the engine run smoother and more effecient. The point is you want your car to idol higher on cold startup. To give you a real world my G is in Southwest Wyoming in normal cold startups below zero regularly and I don't go over what I have said on the RPM scale.

I am maybe thinking that it was the muffler delete on the Coupe that made a higher idol.

If you do a relearn procedure as another member said it won't do anything but make the ECU back to a stock learning more(learning your driving habits) but not making your engine idol higher then what the ECU thinks it should.

I really think your G as it sits now is very normal. Your Coupe and your current sedan had only one difference and that was the muffler delete. It's the same engine and same ECU.

It's not like you went from a M56 to a G37. The Coupe and Sedan Engine and electronic wise are the same(dependent on options)

SonicVQ

You have confused an ECU reset with the intake idle air volume learning. The IAVL does not reset the ECU back to stock.

It allows the the ECU to set the proper idle.

Noogie Lamont

The issue the OP is having has nothing to do with any of the systems. The OPs car as it sits now has zero problems at all. The OP wants the car to idol higher then the factory settings permit.

From what the OP has referenced the only real difference between the previous Coupe and the current sedan was the muffler delete.

Today out of curiosity went to see a friend that happens to have a Coupe as well as a muffler delete(sounds really bad). We are in the 40s today. I asked him last night not to do a startup until I arrived. To my surprise the car did have a higher idol then my car and the OPs car as they sit now. I honestly think the muffler delete may be providing more or less backpressure and causing the engine to idol a bit higher upon cold startup. We measured the RPMs at 1500-1550 using an ELM 327 and the Torque app. This is 200-300 more RPMs on cold startup then my car with the current setup.

So short and sweet it is the muffler delete that caused the OPs previous Coupe to idol higher and since the OP does not have a muffler delete on the current car but another setup the car will not idol the way the OP would like.

So any type of relearn is very mute because the OP wants the car to idol higher not lower or as close to spec as possible.