genosis8703

So i did a bit of digging and couldnt really find anyone that has had this specific issue. When i start the car first thing in the day or when its been sitting long enough to go into its initial high idle i have no brakes. My clutch works perfectly fine. Its just my brake pedal goes to the floor. Its not straight to the floor either it feels like its pulsing as it slowly goes to the floor. Almost like the ABS is kicking on but it is not. The odd thing about this is the fact that this only happens during its warm up phase where it idles higher. If i blip the throttle to take it out of this phase everything works and it back to normal. The brakes are 100% after this. I can turn off the car and start it with no issues. The most annoying thing is the fact I only have that short period while its in its warm up cycle to try and figure out whats going on. I did trace the booster vacuum line to the intake manifold and the black fitting that screws into the intake was backed out about half an inch. re tightening that didnt seem to do anything to help. I did remove it again the put some teflon tape on it. Ill have to see if this fixes anything. I wont be able to know until in the morning. I also tried the old trick of holding the idle higher and spraying the vacuum lines with brake cleaner to see if the idle changed and i got no results. I dont even know if this is viable with newer cars of not, its an old school thing.

Thanks in advance for the help. Also im running on zero sleep so sorry if there is any typos lol.

genosis8703

Bump and update. I had the wife pump the brakes during its warm up cycle and the ABS module is definitely activating. Or at least it sounds like it. Still clueless as to whats going on. I talked to a couple mechanic friends and they were clueless.

genosis8703

Bump

ECaulk

iTrader: (6)

gonna throw out a really simple thing, try bleeding the brakes. No idea if that will help, but at 9-11 years old it could use some new fluid.

jdbaugh1

iTrader: (1)

I don't have ABS but I think you could also try to pull the fuse on the ABS system and see if the problem goes away.

RoelSS

iTrader: (3)

Sounds like it may be the ABS module going out. Does your ABS light turn on while it's pulsing?

genosis8703

I pulled the fuse and the issue wasnt there. Although it was suggested that i take the car out and do some hard braking in case there might be some gunk in the lines since i only drive the car maybe 30 minutes every 2 weeks. I did 10 60-0 runs and the car stopped on a dime. The abs worked 100% with no issues.

No light what so ever. Its the oddest thing. The thing that throws me off is that after the warm up cycle or if i blip the throttle to take it out of the cycle everything is 100% normal. I did 10 60-0 runs and 5 more later and the car stops quick enough to where my eye ***** feel like they are going to pop out lmao. The light was on when i pulled the fuse and went out withing the first 1/4 mile once the fuse was replaced.

It looks like the booster was replaced at some point so i dont think its the original fluid but i might just go ahead and replace it. I feel like if it was a fluid issue it wouldnt stop on a dime and act up all the time. But it never hurts having fresh fluid.

On another side not I tried seeing if holding the idle where its at during the warm up cycle would duplicate the results but it didnt. This is just the oddest thing to me. Ive fixed a lot of issues with my previous cars but non as odd ball as this. Even has my father stumped and hes been a certified tech for 40 years.

jdbaugh1

iTrader: (1)

If you pulled the ABS fuse the ABS module should remain inactive. I know you said you pulled the fuse and that made the ABS work 100% with no issues so I'm wondering did you mean the breaks worked 100% or did you actually slam the brakes hard enough to lock up the wheels and you could feel the ABS module kicking on and pulsating?

genosis8703

Sorry for the confusion. I pulled the fuse and started the car and the issue went away. After that a replaced the fuse. I then went out and tested the ABS to see if it would have any issues (with the fuse in). The ABS worked flawlessly.

genosis8703

So just an update. I am still having this issue. I was told by someone that I should see if the turbo is building boost during its warm up cycle. If it is then I have a vacuum leak. Has anyone heard of this? Also I wanted to unplug the vacuum divert on the intake manifold, would this hurt anything if i did this?

C0balts5

At high idle your going to have a crappy pedal until the idle comes down because your throttle plate is open slightly and your not creating full vacuum like when the car warms up a lil and the idle drops, I'll check mine next time I drive it to see if I notice it too but I've never noticed it because i don't move the car until the high idle drops, I'm old fashioned. I want to make sure the oil thins out a lil bit and to prevent excessive wear on the turbo. Abs will run some sort of self check when you start the car and that's what your probably keeping/ feeling

genosis8703

I am the same way. I dont touch the throttle I just release the clutch enough to get it out of the garage so I dont get noise complaints. I usually wait 5 to 10 minutes from there before I drive. The other day I was doing this and pressed the brakes so I could stop and let it warm up and i just kept rolling and had to e brake it. Never had it happen before in the 5 years I've had the car. At this point no one car really figure out what this weird ass issue so I'm going to just take it in. I currently dont have the time and will probably be trading up vehicle wise in a few months.

jdbaugh1

iTrader: (1)

It shouldn't have to do with your brake booster. The brake booster just assists so you don't have to push the brake pedal so hard. The brake pedal should always activate the brakes even with the car off completely. You could have a bad master cylinder but that shouldn't be intermittent. Air in the line can cause loss of pedal feel but that shouldn't come and go that frequently either. If you unplug your ABS module and leave it unplugged, what happens?

C0balts5

Maybe I don't have any issues with mine because every year I hook my car up to the bg brake flush machine, it pressurize and flushes about half a gallon of brake fluid out through to the caliper bleeder, brake fluid does go bad over time. You get air in the system. Before anyone rips at me for saying that I'll explain. About every 3 years you want to service the fluid, reason being is brake fluid hygdroscopic, absorbs moisture. Over enough time alot of moisture gets into to fluid and lowers the boiling point, now when you get the brakes super hot, the brake fluid will begin to boil and give tiny air bubbles (maybe not enough to actually see). But you may get pedal fade or poor performance.
If flushing it doesn't work then I work then try unplugging the abs like what was mentioned. Then if it goes away more than likely it's a bad abs module IF there is no codes indicating a sensor wigging out. Could be air trapped inside the module

genosis8703

Sorry for the delay i have been in and out of the state. If i unplug the ABS module i dont have the issue at all. As far as codes i have not had one pop up. I drove the car and let it sit for a week and this problem just showed up when i had to swap cars with the wifes and was going down hill and pressed the brakes and i just kept going lol.

jdbaugh1

iTrader: (1)

Sounds like your ABS module is either getting a false wheel speed signal or it is malfunctioning and acting as if it thinks a wheel is locking up. I assume it could be from the sensor or the module itself. Until you can get it properly diagnosed (I would think with the right scan tool you may be able to monitor wheel speed sensors to see if they are reading proper or not) just leave the ABS module fuse pulled. No ABS is much more safe than randomly having no brakes. My Cobalt didn't even come with ABS. Just can't slam on them or they will lock up.