ABS problem every time I step on the brake on the bumpy road, ABS light comes on and start acting up by making vibrated noise and brake pedal actually pushes back towards me, which I can not be able to stop immediately. I almost hit cars in front of me many times. Mechanics were not able to detect ABS problem. They said it might be the ABS control unit. Please help! Thank you for your support.

run diagnostic, check your wheel brg and rotor plate might hav cv grease on it also clean all sensors with brake cleaner

If the brake pedal goes hard right BEFORE the car dies, and not after, then you could have a problem INSIDE the brake power booster. try to verify this next time it dies at a stop, if you can safely pull the dead car off the road into a driveway (or try to make it stall in a bumpy parking lot) - then before you try to restart the car, open the hood, pull off the rubber hose where it's plugged into the brake power booster --> you SHOULD hear a big "Swoosh" of air being sucked into the booster because there's supposed to be a strong vacuum there even after the car stops running. if you get nothing there, your car is dying of an excessive vacuum leak through the brake booster.= bad booster.

This may be a silly response but are you sure it is not your ABS? This is the Anti-lock Braking System that prevents your tires from locking up when you slam on your brakes during an emergency. This helps prevent you from losing control of your vehicle. If any of your tires lock up your ABS will kick in and you will know this when your brake pedal starts to more or less vibrate. Sometimes when this happens your ABS light will come on your dash during the time your ABS is in use. This is a normal response and will happen more frequently when on icy, wet, or unpaved and muddy roads.

check the rotors for scoring,worn rotors will "feel"like the abs is coming on due to the vibration caused.and will account for the extended stopping distance.

How hard are you stepping on the brake pedal? What you are describing sounds like the ABS system activating. When you step on the pedal hard enough to engage the ABS the light will come on, in some cars it will blink. You will also feel the thumping/vibration in the pedal since the system works by repeatedly engaging and disengaging the brakes. If it is happening when you step lightly on the brakes then you may have a bad wheel speed sensor or possibly a bad or miss-adjusted brake switch.

the only thing i can think of as a problem would be brake pad quality. i would get some from the dealer and fit them. if there is chatter going on it can also be caused by low quality rotors or a bad maching job. have them inspected for integrity.

Might check around the big black round muffin shaped chamber adjacent to the master cylinder for a loose vacuum hose or crack therin; the hissing sound seems likely to be the air rushing in as you loose the vacuum that supplies the power to assist your braking effort (power brakes)---as this goes, so goes your peddle until it reaches the actual piston pushing the brake fluid (which should be firm like with non-power brakes).
...maybe have an assistant push on the peddle while you listen with a piece of hose or a stethescope to find the leak (or I suppose the power unit diaphragm could be shot/leaking--hence replacement), but since you said after bumpy road etc, one could hope for a simple dislodged vacuum hose or fixable crack.

There's speed sensors at each wheel. You may have got some contamination in front of one of them... sounds like the abs is trying to compensate for un equal speed at each wheel... and something may be blocking a proper read at one of the wheels...

Pedal meant to vibrate when abs is controlling braking on slippery surface otherwise abs unit fault

This is a (4) four wheel sensor system and more than likely one of them has failed. This will cause ABS module to turn on warning lamp and make the brake pedal 'act up' under the right conditions.This 'acting up' is the ABS system getting a false signal that a wheel is not turning the same as the others when it actually is. Have it scanned for codes and a streaming data scan on a road test under the same conditions that you are experiencing the 'act up' to pinpoint the fault. Hope this helps! Please rate me.