Mine does the same thing.. Your just in the power band for the motor. Honda's have this too but they need v-tec to feel it like we do lol.

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1985 335i
Black on Black coupe 5spd
Tokico lowering springs, KYB struts and shocks, BavAuto strut bars, SPC adjustable camber plates, Ireland Engineering rear toe and camber kit, Sparco buckets, Rota Torque 16x7 fronts 17x9.5 rear, Hella headlamps with HID conversion, all red taillights, MSD coil,M30B35 swap, Mustang GT Injectors, Port/Polish