Ever since I had my g35 Idle has been a little rough, it became even more so noticeable after all the mods done, what is interesting is that in real cold weather bellow 30 degrees car idles much better almost with no rough spots noticed at all. What I mean by rough idle is that engine runs almost as if has cams, runs fine 2-3 seconds then all of sudden a slight stumble is noticed. No driveability problems or CEL on. Idle is at around 650rpms
Anyone know what condition could cause the rough idle to be worse in warm vs cold weather?

 

Reset your ECU see if it helps

 

makes no difference

 

I'm guessing it has to do with your throttle body. When its cold, your car runs better because its getting a richer ratio. When was the last time you changed spark plugs?

 

I changed them to Iridiums 2 years ago, I do have a throttle bypassed but with this mod it usually runs rough on cold starts and after it gets better and its not the case here.

 

What spark plugs are recommended for our cars, how much are they, and where can I find them?

 

The spark plug recommendations are: PLFR5A-11 or equivalent. (2006-Earlier) FXE22HR-11 or equivalent. (2007- Later) Gap is .043 inch (1.1mm)

 

You might want to look into replacing the spark plugs. I know the iridium are expensive but you should change your plugs every 30,000 miles or 2 years. Also, I have had a rough idle recently too. Something was causing my car to idle around 300rpms. I just finished tearing apart the upper plenum and throttle body and performing a thorough cleaning of all carbon. I also took out the MAF sensor from the z tube and used MAF Cleaner and cleaned very thoroughly. I re-assembled and WOLA! My idle went up to 600rpms, normal. Cars are picky....its just one thing out of a hundred that happened to help me. Take it for what its worth.

 

Iridiums should last more than 30,000 I think but even if so I live in South Dakota and drive only 8,000 per year so that should not be an issue, plus why would cold weather have a positive effect on a bad spark plugs if that was the case?

 

I richened up AF ratio a bit at idle seems to help, But I dont know if the computer will override it since its in open loop.