areoblackdog

Hi all,
look for some advise on a problem I couldn't fix... the engine I refer is a VQ25DE on a Nissan Teana J32, i got a kind rpm dropping on idle...it could sound as a misfire but is not! to give you an idea it's happen only when is idling and, let say if i slightly rev it only a tiny bit it runs fine! Example it can be noticed when the A/C disengage and rpm going back to normal idle there is the time got that little shake from the engine as it would sound a cylinder misfiring... I also notice when am out of the car with the engine running a smell of exhaust fumes...not sure if related but another thing I notices is when I crank to start it seams to hesitate starting (when engine is on temperature), it cranks a bit longer then it used to! However while driving can't really notice anything wrong! Not to bothering but I'll like to give u few other detail, the original engine is just been swapped with a 2nd hand one coz of major failure after overheat! This problem it was existing also with the old engine, but only occasionally once in a while. Now its always! The injectors are the old ones, wires and ecu are also still the same as well for O2 sensors.
Spark plugs and coils are been replaced...but didn't help! I wandering what to look next...would it be a problem with Variable Valve timing solenoids? Or eventually Injectors issues? Car is a 2012 the new engine not sure bad the previous parts from the old engine run 300k km...
I will appreciate any comment or idea...Glad to be here,
Thanks, Alex