High idle, goes higher when brake is pushed

[Jason Warrum]

Ok guys and gals…. Need a little bit of direction. 92 Yukon 5.7 Pretty sure it’s a vacuum issue. High idle when starts about 1300 rpms. When I press the brake pedal and let go of it the idle shoot’s up even more about 3-500 rpms. Did a little research and found that a bad break booster could cause the vacuum issue Anybody wann add to this or gimme any ideas if anyone has had this issue. Point me in the right direction. In the process of figuring out how to test booster. The peddle isn’t hard to push down. In fact it seems super soft and I almost had to push the pedal all the way to the floor. My 94 c1500 brakes are much tighter. Any help would be appreciated

 

[Erik the Awful]

Pinch off the vacuum hose to the booster with a pair of vise grips and see if the problem changes.

 

[Jason Warrum]

Pinch off the vacuum hose to the booster with a pair of vise grips and see if the problem changes.

Thanks bud. That will be the first thing I try when I get home. Idk if this helps but before all this started my brake pedal was super soft, so I was gna have the brakes checked anyway. I know if a booster starts to go bad the pedal gets harder. Is there any correlation with a bad brake booster going bad with a mushy (soft) brake pedal. Like when I say soft the brake pedal goes all the way down. Just tryn to narrow down the problem

 

[movietvet]

Sounds like two problems. The mechanical brakes may be out of adjustment at the rear or calipers not self adjusting close to rotor or air in the hydraulic system. The higher idle is likely related to where the vacuum is pulled for the booster. The booster itself may be fine......or not. Any work done to the truck before this problem?

 

[Jason Warrum]

Well That makes sense. So I Just purchased and just goin through it tryn to fix any issues. I know my BIL supposedly went through the brakes so it’s very plausible he missed that. I’m just tryn to work out all the little bugs. 92 Yukon great condition. The soft brakes have been like that since I bought it. So yes I assumed bad brake cylinder or bad self adjusters or something along those lines The high idle just started couple days ago. So yes I tend to agree that I believe it’s 2 different issues. I’m having the soft brake pedal looked at next Thursday The high idle just started like 2 days ago but when that started it idled high for a few min then the idle started to come down to normal. Yesterday I started it, high idle and never seemed to come down. I am a tinkerer I would never say I am a mechanic so if I sound stupid I’m just tryn to get all info I can so I can learn. I gna check the vacuum line on the booster when I get home from work.

 

[movietvet]

If you have a hand pump squirt bottle, like you squirt of plants in the home, fill with water and after the engine is warm and is idling, squirt water in areas to see if that changes the idle rpm's. The water can fill a vacuum leak momentarily and the idle can settle. Concentrate on the intake gasket area and vacuum hoses. You can even squirt along the hose to the booster and where the check valve is plugged in at the booster.

 

[Jason Warrum]

If you have a hand pump squirt bottle, like you squirt of plants in the home, fill with water and after the engine is warm and is idling, squirt water in areas to see if that changes the idle rpm's. The water can fill a vacuum leak momentarily and the idle can settle. Concentrate on the intake gasket area and vacuum hoses. You can even squirt along the hose to the booster and where the check valve is plugged in at the booster

Intake gaskets areas specifically? Between throttle body/intake manifold?

Other places to check? Thank you

 

[Jason Warrum]

First thing I found. Vacuum line elbow. Rest of the is fine. I will swap and update

 

[movietvet]

First thing I found. Vacuum line elbow. Rest of the is fine. I will swap and update

Found that with the water trick or just by checking with eyes? Is that a feed for the brake booster or what?

 

[evilunclegrimace]

Found that with the water trick or just by checking with eyes? Is that a feed for the brake booster or what?

It looks like the PCV connection. The brake booster connection comes from the front of manifold through a preformed steel line that transitions to a rubber line at the booster elbow.