Drive it hard. There may be carbon buildup inside one or more of the combustion chambers causing a poor idle. It can happen easily if you have excessive oil dumping into the intake ports (usually 5 is the worst) from the PCV system and/or a bad injector.
E92 335i/6MT Dinan Stage 3: intercooler, oil cooler, intake, flash, exhaust, LW dual-mass flywheel.
Vishnu PWM methanol custom trunk mount, Diffsonline 3-clutch Salisbury custom diff, Ohlins Road and Track coilovers, Vorshlag camber plates, much more...
E28 M5 w/ buncha stuff, R171 SLK350