Lamb

Guys, My best mate took the plungs last week and bought a black P reg VR6 highline.......lovely car with 98k, full history etc etc...... Car is running a Ram air fliter and Miltek exhaust. Now the car seems to bog down/hesitate at low revs but seems to clear once he puts his foot down..... Car starts, runs and drives perfectly otherwise......it seems to be at low revs when he is pulling away. Any ideas??