ok so i was driving down the road & came to a stop i noticed my tach pulsing up & down about 500rpms when i took my foot off the brake it stoped but it was idling a little high i checked the vacume hose to the power booster & didnt notice any leaks the guy at the auto parts store was trying sell me a new booster. i did notice what looks like a check valve inline on the hose could this be my problem? or do you think my booster is bad? i dont hear any vacume noise coming out of my booster. just want some input before i shell out the cash for a new booster

 

Soooooo you should probably give some info like what vehicle you are driving and the motor at minimum, and before you post you should do a search of your problem.

https://www.yotatech.com/forums/f116...ressed-231139/

This is just one post, search and you will find lots and lots on this issue.