Strange thing going on

[mm58]

Hello group

Driving around lately, I have noticed my RPMs going up a bit after I come to a stop.
I could take my foot off the brake and quickly stab the gas pedal and the RPMs would
briefly return to normal, but then quickly rise again.

Today I became aware that it was the action of pressing the brake pedal that was somehow causing the RPMs to climb.
* Foot off the pedal and normal idle RPM.
* Just barely touch brake pedal and slight rise in RPM
* Press hard on brake pedal and RPMs climb even higher (Maybe 100 rpms?)

Wondering if anyone else has experienced this and what you found to be the cause.
I haven't even begun to look under the hood yet.

Just curious what you all think might be going on.

Thanks...

[ChickenPinz]

I would start your debugging by disconnecting the vacuum hose that goes from the engine to the power brake booster. Close it off at the engine.

You may have booster diaphragm leak.

[Jim LaGuardia]

Replace the brake booster.
SAV has a great replacement.
Also replace main vacuum hose.

[mm58]

Thanks guys for the feedback!
I've just ordered a new booster from SAV.

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[ChickenPinz]

Watch for rub points on the hose -- I added a p-clamp in one spot, and a metal sheath where it penetrates the body sheet metal.

[mm58]

I received my new brake booster today from SAV, and in the process of replacing it, I find the original booster half filled with brake fluid. What a mess!

I'm assuming now that I need a master brake cylinder rebuild kit (??)

Mike

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[Tjerk]

Yes, you do!

[pinzinator]

Years ago I replaced my booster and it was like driving a new Pinzgauer afterward. The engine ran normally, the booster just wasn't working to potential for some reason.