My Primera has about 95,000 miles on the clock. It has two problems - the first is the idle sound, which oscilates a bit and sounds like it has sudden attacks of 'mosquito-like' changes in frequency.

Vibrations are not an issue and idle speed is good and constant. The 2nd thing is that it is unable to achieve top speed on straight road and it is too early for the engine to loose much of the power and die. It revs in 6th until about 5000 and like it has some blockage in that spot, the needles are unable to move forward.

Even in fourth gear you can feel a bit of laziness after 5000 revs. Spark plugs changed, ignition coils seem to be ok. What could it be? Local garage put a blame on injectors primarily and suggested a check and replacement if necessary, or cleaning.