bad idle at times

[lockmup]

I have a 97 ranger 4.0 litre 115,000 miles runs great,cel came on codes po171and po174,replaced 2 o2 sensors reset light,cel came back on next day same codes,truck ran great,so figued what the .... now my son is driving it and it starts to idle rough at times and go dead when stops sometimes,it will idle rough shake then die.cranks right back up.have replaced IAC and looked for vac.leaks cannot find any.it seems to idle fine then if you pump brake it starts idleing rough dont have any clue...any help appreciated

 

[smokey]

Sounds like you MAY have a ruptured Brake booster. It sounds like it is creating a vacuum leak when you pump the brake petal.

 

[lockmup]

thats what i was thinking. is this a common problem?