Problems with rough idle when hard braking HELP!!!!

96xj 4.0 just little over 200k

just trying to pick some brains on wtf is with my jeep.. had an idoit jump in front of me and I had to lock down on the brakes but when I did the engine started to stumble and smoke and had a good bit of a knock to it.. pulled off the road and switched it off.. switched it back on and used obd2 adapter to check for pending/logged codes and got a code for injector #4 sticking so I poped open the hood and looked at the connector just to make sure and it was fine but i also noticed that the brake fluid was dam near empty and I just filled it a week prior.. started it up after topping off the fluid and it ran fine no knock or smoke .. now I've got some 4port injectors from k suspension and im going to change the rear wheel cylinders to make sure there's no leaks there but has anyone ever seen this before?? Someone said it could be the brake booster and best way to check is to pump the brake firm hold it and start the jeep with it held and if it kicks back or doesn't want to move the booster needs replaced.. well my brake fell nice and smoothly to the floor but it has a bit of a woosh sound and after I continued to hold it down that stumble came back.. it wont do it just average braking at lights and such just when i push the pedal all the way down with force.. someone also mentioned a check valve could be causing the stumble and the loss of fluid..

I have a big road trip in a month and trying to figure this out before then and you folks have had more jeep experience that my local backyard mechanics that work on gms daily lol


I AM NOT A MECHANIC BY ANY MEANS BUT ANY HELP TO POINT ME IN THE RIGHT DIRECTION WOULD BE GREATLY APPRECIATED

Your brake booster is very high on the list! If your losing that much fluid and not seeing puddles, then it's going inside the booster, seen that many times. Be aware of all the complaints with K fab injectors and the rest of their products.

The booster could be OK, but is getting a load of fluid out of the master cylinder and the brake fluid is obviously getting sucked into the the engine by the vacuum line to the booster.

Thinking about it, the master cylinder has to be bad. The only way fluid is supposed to be able to get out of a master cy is through the ports where the brake lines attach. Yours is obviously giving up fluid where the master cylinder body is bolted to the brake booster. It pretty much has to be leaking around the main piston where the brake rod from the booster pushes when you push the brake pedal. The booster may also be bad if it has been ingesting brake fluid for a while.

Laggin Lycan said:

96xj].......my brake fell nice and smoothly to the floor but it has a bit of a woosh sound and after I continued to hold it down that stumble came back.......

Click to expand...

Yep, both the master cylinder and brake booster are bad.
The good news is that they are easy to change, and you
don't have to work underneath the vehicle....

I've always wondered about my jeep stumbling under hard braking. Thought it was in my head. but maybe my booster/mc are on their way out too.
Thanks lol!