Why does my Nissan SR20 idle bad but when i rev it to about 5 and a half it just idles bad when i rev it normal while in 900rpm idles good not at 5 and a half?

A rough idle at higher RPMs while your Nissan SR20 runs smoothly at lower RPMs could indicate issues such as a vacuum leak, dirty fuel injectors, or a malfunctioning idle air control valve (IACV). These problems can disrupt the air-fuel mixture or airflow, causing instability at higher revs. Additionally, check for any ignition system issues, like worn spark plugs or faulty coils, which can also lead to poor performance at elevated RPMs. Conducting a thorough diagnosis will help pinpoint the exact cause.