Hi everyone. This has been bugging me for a few years now. Whenever I shift the car into D, the rpm dips (when I'm a stop light for example, so the car is idle), to the point where the car feels rough, and things vibrate a bit. I've learned to just put up with it, but I'm trying to figure out the problem. Car drives fine besides that, engine has never stalled, no engine codes.

Things I've ALREADY done:
-Cleaned MAF
-Cleaned throttle body
-No ECU error codes, or air leaks, that are at least obvious to detect
-Reset ECU
-Attempted an Idle Air Volume Re Learn (no idea if it worked), I even tried using the NDSIII app, but I kept getting 'ECU Busy..please wait'

Does anyone know what the spec (normal) RPM is for a G37x (2010 model)

I used an odb reader and I found that the RPM at idle (when in D) is 550. Is that technically normal, and in spec?
When in P or N, it goes up to 700 something, and the sound and vibration isn't as bad. Most of the sound/vibration is coming from right under me, and I'm pretty sure its the cats, hoping its the heat shield.

So what else should I absolutely trouble shoot next, as in it may be a high probability cause? I haven't asked the dealership about it yet, but my last visit to the dealership they said I need to change my rear differential oil (its past due), would that cause a rough idle in Drive?

EDIT: Found this video on youtube, is EXACTLY what my car sounds like. Hopefully that helps...

 

Cam position sensor perhaps?

 

Hm, possible. Wouldn't that throw an engine code though?

 

I read in the service manual idle speed (in P or N) should be 650 +/- 50.

Cant find anything about what it should be when in Drive. Can someone kindly get a reading from their car and let me know. It may very well be that 550 is normal, and there is just excessive rattling/vibrating from the heat shield or something, I'm not sure. Although it does sound like some diesel engine to me, and judging from the above video, I'm starting to think it is the fuel damper.

 

On my way to class so here you go my idles is pefectly smooth.

 

Thanks, OK that is like mine. So the idle RPM is normal, its just that mine isn't smooth at all. I'm almost 100% sure its the fuel damper then. I hope it doesn't cost much

 

so did you find a way to fix it or cause of the rough idle? My car has the same issue was it the fuel damper? If it is and you fixed it where and how much did they charge you?

 

Try changing plugs & oil. Has it always made the sound or new? Which oil use to change & has car been in accident before?

 

perhaps one of your motor mounts or related drivetrain dampener is worn or collapsed, hence the vibration at idle.

 

I had the same issue and got my throttle bodies, MAF, and Fuel Injectors cleaned out. The sound is gone and the acceleration is much smoother.