idle fluctuating when my truck's brakes are applied coming to a complete stop. Please help!?

gadawg8111 · February 6, 2023

I've owned my 2011 Silverado for almost 2yeatrs I bought it pre-owned in July of 2021 with 98k on the odometer. The truck currently has 125k on the odometer and hasn't give any problmes other than the fact that the truck surges/lunges feels like it is rocking forward bath and forth while applying brakes coming a complete stop. It does this back and forth motion 3-4 times before coming to a complete stop. The rpms are moving up and down during this breaking cylce before coming to a complete stop. I've experienced this issuie in a much lower level until as of recent as a result of swapping cam for BTR truck norris in addition to AFM and VVT delete. I just replace the Vaccum brake booster assembly, brake booster sensor and new brake stoplight switch hoping that might solve the problem. Also, I replace the thottle with a new oem and it has gone through the re-learn procedure. Lastly, the truck was dyno tuned after the BTR norris cam and other goodie were installed. Does any have any additional reccomendations as to what is the cause of ithe dle fluctuating when myu truck's brakes are applied coming to a complete stop. I would greatly appreciate any and all insight as to what my issue is and how to go about correcting it!

Kind regards,

Brandon H.

Thanks so very much!

asilverblazer · February 6, 2023

If it is a vacuum leak - try hooking up a gauge - I'd go back and review the replacement of the booster and lines.

You're not feeling warped rotors are you?

gadawg8111 · February 6, 2023

shifting out of park when im pressing down on brake pedal and lef off of it and press again firmly it feels as if it is stick almost stuck for a moment and then goes away. Iv'e been having this problem on a much smaller scale for the majority of the time i've owned the truck. The issue has worsened since the bigger cam has been installed. I followed the brake vaccum booster hose with my hand to where it connects to the intake manifold and tried to push it more snuggly and the trucks ilde changed while i was doing that. I had a friend inside of the truck watching the tachometer. I'm not sure what exactly to call the piece on the back on the intake manifold that connects the vaccum brake booster hose. Any idea what that would be called? I also had a bolt from the factory missing from the maf meter that was replaced by previous owner with one of a differenet size and thread size. I noticed where the bolt attaches the plastic was slightly cracked from the bolt being to big. I'm wondering if that could be one of the culprits as well. Thank you so much for replying to my post! Hopefully I can get this issue solved!

dna9656 · February 7, 2023

I'd replace that component with the wrong size screw, then AFTER testing all the hoses for leaks look for cracked rubber hose, split hose, cracked split, broken vacuum fittings. Any question about the hose or component, replace it with a new one and include clamps to insure integrity of the vacuum signal. Wire (zip) ties an make great claps if you have a pliers like tightener for them. Check your local Harbor Freight for this tool.

asilverblazer · February 7, 2023

20 hours ago, gadawg8111 said:

shifting out of park when im pressing down on brake pedal and lef off of it and press again firmly it feels as if it is stick almost stuck for a moment and then goes away.

The first pedal push is using up a majority of the vacuum in the reservoir, the second press doesn't have enough, as the vacuum builds it the stuck feeling goes away.

20 hours ago, gadawg8111 said:

Iv'e been having this problem on a much smaller scale for the majority of the time i've owned the truck. The issue has worsened since the bigger cam has been installed.

The new cam that is probably more aggressive won't develop vacuum like the factory. It has exaggerated the problem.

20 hours ago, gadawg8111 said:

I followed the brake vaccum booster hose with my hand to where it connects to the intake manifold and tried to push it more snuggly and the trucks ilde changed while i was doing that.

Sounds like you found A problem causing a vacuum leak.

20 hours ago, gadawg8111 said:

I also had a bolt from the factory missing from the maf meter that was replaced by previous owner with one of a differenet size and thread size. I noticed where the bolt attaches the plastic was slightly cracked from the bolt being to big.

Might cause other drivability issues, probably a lean condition in the engine. The cracked plastic will need fixed plus the correct bolt put in.

If memory serves there should be a check valve in the vacuum line to the booster, I'd check that too.