I just noticed a weird issue on my truck. When it's in park and idling, if I step on the brake pedal the rpms go up to around 1200, and then settle back down to about 6-700. It does this everytime I step on the brake pedal in park. It's odd though, it's almost like I'm stepping on the gas slightly everytime, and no, I guarantee I'm not stepping on the gas. Any ideas why it does this?

Thanks.

 

something about the vacuum booster, not sure exactly why though.

 

had the same problem on a saturn replaced the check valve on the booster and fixed the problem