This was exactly why I got rid of my open filter I lost power in low down revs and from a standing start. Its down to heat soak and unless you get a good cold air feed there is nothing you can do :up: Either get an enclosed system with a good cold air feed or get a panel filter to use in the standard air box.
depends on how you fitted your K&N, if on the throttle body it can reduce power specially if there's no air feed, if you run the K&N towards the battery it is better as there's less hot air. On mine its not noticeable but thats cos of the bonnet vents letting the hot air out.
It dosent matter if you have an air feed the size of a dustbin, you will still get heatsoak and the lag that you are describing.
With an 'open' filter when you are stationary or travelling very slowly, then there is no airflow into the engine bay or into the cold air feed, so the filter will draw in the hot air surrounding the engine. Thsi is what is known as heatsoak and it will also affect all the pipes and ducting as well as the plenium chamber.
The engine will not suck air from the pipe unless it is totally enclosed as in a closed system.
I have had the standard system but with a pipercross performance panel filter, an Apiero Aeira and now a closed carbon fibre Diavolo to which I have also added a mirrored stainless steel heatshield for cosmetic reasons as well as to help reflect some of the radiated heat from the engine block.
The open filter made a gorgeous noise but I suffered horribly with lag and stagnation on acceleration. The panel filter made little noticeable difference but showed about 2 hp at the wheels increase. I have yet to dyno the closed system to see what (if any) improvement this has given.
If you want decent acceleration, you are going to need to ditch the open filter system.
I dont think that the K&N is actually slowing your Rev counter down as all that indicates is RPM. What the K&N is slowing is your engine which is being correctyl reported by the RPM gauge and thefact that you have sluggish acceleration