Nissan Repair: High idle at cold start problem - R34 Skyline RB25DET NEO, skyline rb25det, air inlet hose

Question
Hi Von, I recently pulled apart my r34 skyline rb25det neo to replace rocker cover gaskets and plugs. I now have a very high cold start idle 2000rpm. I have replaced the MAF, O2 Sensor and am about to pull apart the IAC unit. Another strange thing is that when the car is warmed I get a good idle of 800rpm again, but when I engage a gear, any gear the revs go straight back to 2000rpm? Any ideas on what is causing this one, a bad earth somewhere, or a hose cable has come loose? I have been over the car so many times and cannot work this one out,and have checked for leaks etc but cannot find anything. Could spark plugs gapped a 1.1 cause this issue, this is the standard plug gapping, but I read that some people use 0.8mm? please help I am at my wits end trying to resolve this one.

Regards

Simon

Answer
Simon,

I will almost bet you have a vacuum leak that is causing the problem.  Check the air inlet hose where the air meter and the throttle body connect.  If there is a loose clamp or a crack in the hose you will get too much air and that makes the car dump gas and the RPMs go up.  The sparkplugs will not cause the problem.  Also, if there is a leak on the valve cover gasket or any vacuum hose.  I would check these over too.