This is horrible...it more annoying than anything else... wondering if anyone has any idea!!! vI have an 88 Pick Up with a V6. When I put my foot on the brake the engine almost dies, then revs back to just above idle, the almost dies. It will do this continuously until i take my foot off the brake. I thought it was the brake booster so i replaced it and the master cylinder.... to no avail. I pulled off the vaccuum hose going to the power booster and hit the brake pedal and it still does it. So i think i reaplaced the booster for no reason... HELP PLEASE!!!!

 

Did you check the brake light circuit? Maybe some wires to the ignition/engine control system are crossed somewhere. Try disconnecting the brake light switch. I hope something works. Good luck.

 

well thanks for the idea.... i will have to check it out!!!

 

ok after some diggin in the site i actually found the problem.... its and idle problem for anyone wondering. solution can be found here:
http://www.geocities.com/toyotashawn/bizzareidle.html

 

also check for any vacuum leakes going to the brake booster

 

I had the same issue a couple of years ago. The culprit turned out to be a crack in the air intake, right at the throttle body. The air flow is measured at the air filter - if air seeps in before the combustion chamber it causes a problem (according to the EFI computer). Stepping on the brake pedal reduces the fuel flow to minimum (don't need extra fuel and brakes at the same time, right?), but the computer may says that more fuel is needed based on the airflow, hence the neverending loop while you're on the brakes.
This problem drove me nuts because it would happen, I'd tear apart everything and put it back together tightly and the problem would be gone. A day or three later, it's happening again (after heat and vibrations had opened up the crack again).
You should also check for vacuum leaks anywhere else in the system. They can cause similar problems.