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Feb 5, 2018

Rough Idle or High Idle : Nissan Skyline GT-R : RB26

An RB26 should idle smoothly at around 1000 rpm on the tach. There should really be little vibration, or noise, other than what a 25,27 year old solid lifter engine makes.  Which in reality is pretty loud with the hood open.

R32 GT-R Speedometer in miles per hour
Most of the time, if you hear a noise, that sounds like a really bad lifter, it is normally the bottom end on an RB. However, troubleshooting that is a different post.

Troubleshooting a Rough or High Idle Nissan Skyline GT-R

  1. Observation is key
    1. It is important to have a look at what a car is doing. Open the hood, look for anything obvious. 
  2. Once you have had a cursory look under the, hood, make sure you have gasoline( had this happen to me recently), make sure the fuel pump seems like it is running, no crazy amount of smoke out the exhaust, onto the next step
    1/2 a tank of gasoline
  3. MAF
    1. Are they plugged in?
    2. Do the hoses look OK? 
    3. Give them a bit of a tap with your hand, does the idle rpm change?
    4. If yes, then proceed to MAF troubleshooting page
      MAF with HKS air filters
  4. Vacuum leak
    1. There are lots of spots to have a vacuum/boost leak. 
    2. Large intercooler hoses
      1. There are the top intercooler hoses that are visible, plus the ones that run though the fenders to the intercooler. If these come off the car will idle rough and spit black smoke out of the exhaust. 
    3. Around the injectors
      1. The lower injector bushings can get crispy and shrink over the years. They are rubber and get hot. Sometimes just giving the injectors a twist will reveal an issue. 
  5. Throttle plate adjustment
    1. Three sets of two throttle bodies
    2. Individual adjustment
  6. TPS adjustment
    1. If the car doesn't know it is at idle, you can have some idle instability. 
    2. It should be appropriately 0.5 v at idle
    3. It should be approximately 4 v at WOT
  7. IAC adjustment
    1. Idle Air Control
  8. AAC adjustment
    1. See below.

AAC Adjustment RB26dett Nissan Skyline GT-R

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1 comment:

Anonymous said...

I also experienced rough idle because of the TPS harness socket connector. When we moved the connector a bit the idle changes. Maybe the terminal pins needed some looking into. :)