I figured I'd post this here because I'm out of ideas. My car right now is idling at ~1200rpms when it's fully warmed up and will idle a bit lean, often hitting low 15 AFR's. Cruising is fine and smooth in the 14's. According to my wideband it gets pretty rich closer to redline @ WOT, around low 10's and I know the car was tuned for low 11's. EMS is a UTEC. Could it be a bad PCV?

 

VAC leak will cause low/bumpy idle.

 

not on my z, but on my truck, throttle kept sticking at high idle, so I disassemble the throttle body unit and lubed it back to normal. and yeah.. leaks will give you low idle. Is your temp normal?

 

Yeah temp is normal, has never overheated.

 

A small vac leak can cause a high idle.The best way to find it is get some carb cleaner and spray it around all vac hoses..intake..throttle body etc to find it.

 

does it rev between shifts when your foot is off the gas?

 

No, just stays at 1200

 

i had that problem befor and it was the throttle body
i got a new one and its fine now

 

Perfect...

 

I thought about this today and it can't be the problem. A bad TB wouldn't cause my idle to go lean.

At times at idle while at a red light it will get so lean 17:0+ that the engine will start stumbling and stuttering and then go right back to 15:0

 

Did you check your Plenum bolts, mine came loose and caused a leak a huge leak the same thing happened RPMs went crazy

 

Mine does the same thing but only on initial startup.....then it goes away and never comes back.

 

Yes I did, and I figured since I was gonna loosen/retorque the bolts I might as well throw a polished one in there, so I did. Put it on, torqued to spec, problem still there. I think I'm gonna try the carb cleaner thing next. If that doesn't work, back to the shop it goes

 

you should also clean your MAF sensor that could do it too

 

Now THAT is a good idea, thanks What should I clean it with?

 

sorry for the noob question what is a maf sensor and where is this located? thanks.im getting the same problem rpm is going crasy like im not even feeling any power on my z its just like reving when im on 2 and 3rd gear?thinking about a leak on my muffler or maybe my nismo intake?

 

Go to the dealer or find someone with a consult II/III and do the idle air volume learning? Maybe that would help. Or since you have utec perhaps you need to mess with the values in the 0 column since you dont have stock injectors they need to be set to some number in the negatives.

 

Mass Airflow Sensor, its on the intake tube, if you look on the intake tube you should see a rectangleish box with a wire harness plugged into it. Its attached with 2 screws, torx I believe. Dont touch the wire ^_^ clean it with a spray to clean electrical parts, im sure you can get it at an autoparts store or radioshack.

 

Advanced auto sells mass air flow cleaner its like $5 just let it dry good and hold it by the plastic, be careful they are like $300 or more to replace, its always a good place to start, and Disconnect the battery, if you dont you could throw a code

 

I got the CRC MAF Sensor cleaner today and cleaned it when I got home. I let it dry a while, put the sensor back in and the rough, high idle is still there. I knew it would've been too easy of a fix