I'd like to say hi to everyone. This is probably my first post here after a long time joining, so any help would be very appreciated. The post is rather long because this case I can't find the answer from other posts here. I'll describe as much info as I can so you can grab the picture.

First is my location, I live in Ho Chi Minh City, Vietnam, heavy traffic jam, average speed of 20-40 MPH, humid weather, currently in hot season (100 deg F at 12 noon, avg of 86 deg F). My car is a red 08 G37S Coupe (12/2007) with all options, incl 4WAS, completely stock, US Specs, only 39k miles, all in pristine condition, engine barely makes any noise in idle. The only problem with it is the surge when braking. However, it's more like an extended version of it. It happens when the engine gets really hot and it has this very same pattern before it happens: I'll sum it up in points below:

1. Car drives fine when engine is cold. I always drive for 10 mins before turning on AC.

2. At first, outside temp sensor shows correct number. After turning on AC, outside temp sensor starts rising, let's say true outside temp is 86F, sensor will always show around 95F and stays there for a while. If driving speed is low, it then keeps rising higher. Once it reached 122F while outside was only 86F. If I turn off AC, sensor slowly goes back to true temp and all is fine again. Pls note: NO ENGINE OVERHEATING whatsoever, coolant temp stays half way always, only cooling fan is at max speed. Coolant is always between 176F to 212F, which is acceptable.

3. With speed from 50 mph or above (in highway), even with AC on, temp sensor is correct and no surge when stopping at all.

4. As outside temp sensor number rises, I have to prepare for the surge. Before the surge, in Drive with no gas, RPM will stay at 1200 RPM, feels like it's compensating for something; but with brake or in N, RPM stays at 700, nothing happens. Once in D, it will rise to 1200 RPM and car crawls faster the normal.

5. When the surge happens, whenever I come to a stop, car would surge terrifyingly forward, RPM surges also, I have to step heavily on the brake to prevent it. That works most of the times, car stay stills, RPM drops back to 700. In extreme cases, even with brake on, it jerks like hell, RPM goes up and down rapidly, feels exactly like a crazy horse trying to run forward. In those cases, I shift to N, all back to normal . Again, turning of AC solves all these problems.

6. Car has new MAF sensors, thoroughly clean throttle bodies, new genuine air filters. New MAFs and clean throttle bodies did help for like a week, then problems came back again till now.

This pretty much sums it up. I've been noticing this problem for nearly 3 years and it now gets worse, but still same pattern.So please, if anything, pls advise me. This must have something to do with the temperature but I can't figure out why and how. There's no fault code in all the ECUs from my Autel scan tool.

 

The ambient temp sensor does read high normally. When stopped in traffic I'm not surprised it spikes as it's not really outside the car but rather in the lower part of engine bay. The vq normally runs hot. I would say heat soak is your issue. If you can read live data you'll see oil temps in the 220s or higher. My 08 cruising ambient 70 runs in the 230s even with oem oil cooler. I'd look into a thermostatic oil cooler and cold air intakes

 

It is perfectly normal for the outside (ambient) temperature sensor to read higher than actual temperature- especially in hot stop-and-go traffic. The ambient sensor is located behind the front bumper. When you are not moving hot air/heat from the radiator, fans, and engine (plus the cars in front of you) builds up behind the bumper and throws off the sensor readings. Once you are at speed and have fresh, cooler air moving across the front of the car, heat is being rejected normally and your sensor is reading accurately. Again, perfectly normal.

Please note, the AMBIENT (outside) temperature sensor has NOTHING to do with your engine or your idle issue. The ENGINE COOLANT TEMPERATURE sensor (mounted on the back of the engine) can play a role in maintaining idle.

Under certain conditions if the engine starts to get hot, the ECM will slightly raise the idle to increase coolant flow (the faster the engine runs the faster the water pump moves coolant). Again, this is normal but your idle should not be as high as 1200rpm which leads me to my experience.

I had a erratic idle issue. All would be normal then suddenly- and without reason- the idle would hit 1100rpm. The problem was worse when braking to a stop as the car would lunge forward. Once in P or N, the idle would only settle to 900rpm and once put in D it would want to jump off the line.

In my case, I found out that Infiniti had issued a Technical Bulletin for this exact issue (ITB 07-048B). I do not know your VIN, but your build date (12/2007) falls right in with this bulletin. This required the dealership to reflash my ECU. The dealership did this back in 2012 when I had roughly 45K miles and have NEVER had a idle issue since. My cars idles perfectly at 650rpm with or without the AC on. On really hot days the idle might hit 680-700rpm, but that usually only happens when stopped at a red light or at my banks (infamously) slow drive-thru window.

Here is a link to the service bulletin pdf: ITB 07-048B.pdf

Not saying this is your issue, but it falls into line with your symptoms.

Hope this helps!

 

Definitely check for that recall reflash first.
Definitely add a transmission oil cooler with fan. Don't need a thermostatic adapter as the transmission already has one internally.
As the cooler(s) won't be able to do much while you're sitting in traffic without that fan.
Definitely add a thermostatic engine oil cooler, with fan.
Look into deleting the coolant lines at the throttle bodies And at the engine oil filter.
Clean your throttle bodies, and do the idle air relearn dance.
Finally, enjoy your now much cooler VQ

Note: there are DIYs written up for all of the above

 

@All: I see, thanks a lot for your advice. The TSB I do know about it, my VIN is in that TSB, too. I just thought my case is more extreme. Since ILM-NC G37S pointed out a similar case, I believe TSB is to be solved.