Hello, I have been a member for awhile, but this is my first post. My 2005 G35 Coupe has a rough idle. I have looked at many threads regarding rough idles, on both g35driver and my350z forums, but have found nothing that has fixed my problem. So I thought it was time to make a thread on my specific situation.

The problem is that my rpms drop at idle, then the car shakes for about 2-5 seconds, then once the rpms raise back up it starts to idle normal again. This happens maybe about every 40 seconds or so, not in consistent intervals. When I am driving the car, I feel no power loss or hesitation. At Idle, when I turn the AC on i do not experience this rpm drop/ rough idle.

Things i have done/replaced:
Cleaned throttle body
Idle relearn procedure
Cleaned MAF
Replaced all coil packs
Replaced all spark plugs
Installed 4 new o2 sensors
Cleaned inside plenum (after installing catch can)
Checked for vacuum leaks

One last note, during colder temperatures in the winter, upon starting my car, the brake pedal is very stiff. Its so stiff that i cannot push it down and the car will not brake if i tried. After about a minute of warming up and pressing on it, it will finally sink down, and then i can brake normally. Furthermore, when I turn my car off, I hear a whistle/pressure being released around the brake booster area. I am not sure if this is related to my idle issue or not, but I am just mentioning everything I can think of.

Does anyone have any ideas? My best guess at this point is a vacuum leak, but i have looked and found nothing. Thanks for your time!

 

Hmm, when my g35 idled rough my engine threw the code P0113- Intake Air Temperature Sensor 1 Circuit High Bank 1. Is your engine throwing any codes/lights? If you have access to a scanner, the first thing I'd do is scan it and see what the engine is trying to tell you. Otherwise stop by an auto parts store, most of them do free scans.

The second thing I'd recommend is just going through and checking all connections to your sensors, and tightening all the connections between the air intake/throttle body. See if your air filter is dirty/clogged. Just the basic stuff. That's what did it for me.

 

Thank you for your reply. I do not have any engine codes, and have not ever since this problem started. At the shop where I work, we have a pretty high end OBD2 scanner. Ive used that multiple times to see if there was any codes that were not popping a check engine light, and it showed no codes.

Also i have checked many, if not all, connections of sensors and vacuum lines. I will go through once more throughly to rule that out.