bobbing idle

[knowleqe]

hey everyone, my problem is this: whenever i start braking lets say in 5th with the clutch in, my rpms will dip to about 200-500rpm w/the AC on. if i were to go to neutral, THEN, brake the idle will stay at 650rpm. but if i brake and have the clutch in at the same time is when the rpms will dip dangerously low. i am going to remove and clean the IACV valve this coming tuesday and change the O2 sensor since i am also getting bad mileage, 150mi at half. the vacuum lines coming from the intake are all secure. what do you guys suggest that i look into?

thank you