Nissan Repair: help with r33 skyline rb20e, synthetic gear oil, noid light

Question

my baby hi,hope you can help
i bought the car a year ago and immediately noticed that even when the car is warm it idled way too high(1600rpm)!!
i have cleaned iac valve, checked and opened the cold start valve also.....idle screw on iac is wound in to the last and i have the little shutter on the cold start valve permanently closed.....in doing all this, the car now idles at 1400rpm when car is cold... but jumps back to 1600rpm when she heats up!!! going insane trying to find it!!
also i replaced the clutch plate, clutch cover and bearing with genuine nissan n/a parts.... since doing so , on the release of the clutch there is a constant whirring sound coming from the gearbox area, which disappears when i hold the clutch in?????

would greatly appreciate some help
thanks
richard

Answer
Richard,

A way cool car!  On the high idle I would check for leaky injectors that would lead to a high idle.  Too much gas means the computer has to compensate to keep the engine running.  You have addressed all the usual suspects regarding a high idle based on the idle air control valve and minimum air setting.  Now, you could have a vacuum leak that you have not discovered like a blown vacuum booster.  So, check the fuel pressure while at idle and then turn the engine off.  If the pressure drops off really fast then you have a leaky injector or two...  A noid light or a volt ohm meter is not going to help you discover if an injector is stuck open.  But, it would aid in figuring out if it is out of range so check this too.  Now, for the vacuum booster for the brakes.  Unplug the hose and cap it and if the idle drops you will know if the booster is defective.  

The noise you hear while the clutch is out is the imput shaft bearing.  You have a haul ass car and that much torque will kill bearings over time.  Also, starting the car and warming it up hurts the input shaft bearing since it gets no oil until the car starts moving.  I would suggest changing to synthetic gear oil and see if that makes it last.  But, eventually you will have to replace the input shaft bearing and race and the noise should go away.  Genuine Nissan bearing or a Timken bearing.  rockauto.com or courtesynissan.com are both good sources for parts if you can wait...