Standing on brake causes rough idle

[Phishin]

I am not sure if this is typical/standard behavior or if what I am seeing is pointing towards a problem.

But with my truck at a stop....if I stand on the brake and hold it there long, the RPM's drop and the truck begins to idle roughly.

I know for sure it does this when it's in park. And it does it at gear, but not as noticeably.

Is this common or is this pointing towards a vacuum leak somewhere?

I'm talking about the truck in my signature btw.

 

[zloveraz]

check the brake booster...

 

[SS1970chrysler]

sounds like a vacuum leak to me.

 

[mac5150]

your sucking air from the engine. its normal to a point . your situation sounds a little excessive though.

 

[Chris142]

Leaking brake booster.

 

[demarpaint]

Vacuum leak.

 

[mechtech2]

If you have a vacuum booster brake assist system, excessive leakage can do this.
Also, brake lights take a bunch of amps, and with some vehicles, you can feel the load increase at idle.

 

[brelandt]

Originally Posted By: mechtech2
If you have a vacuum booster brake assist system, excessive leakage can do this.
Also, brake lights take a bunch of amps, and with some vehicles, you can feel the load increase at idle.


I've been thinking along this line for my truck. feels like a sudden load had been placed on the engine and it was caught off guard. the idle picks back up within a split second however and never dies.
could be this?

 

[Phishin]

Originally Posted By: Chris142
Leaking brake booster.


If I have a leaky brake booster of another leaky vacuum line somewhere, is there a way to help diagnois this problem or the exact source of the leak?
It's probably not even worth finding, because the truck never stalls. I can just tell that it doesn't like the brake pedal pushed to the floor very long. LOL!!

Or is this leak likely to lead to a bigger problem and needs addressed now?

 

[mechtech2]

There is some leakage allowable.
[When the pedal is depressed.]

A quick test is to pinch the line to the booster - close it off completely. If you note an idle change, it is leaking too much.