brake booster

[1990LTD]

I'm trying to figure out if I have a leak going to the booster or if the booster itself is faulty. When idling in park, I put my foot on the brake and there is no discernible change in idle, but when I release the brake, the idle surges very very slightly.


Sometimes it's not enough to notice unless I'm looking at the tach when doing so, but sometimes it is enough to feel.


Normal? Indicative of a leak in the brake booster?

[1990LTD]

Figured out that the harder I push on the pedal (the further I push it down, I should say) the higher the idle surges when I let off.

[sly]

sounds like a booster check valve or grommet is messed up or the booster may have a bad seal (rust hole?) somewhere (aka leak). Can't think of any other reason for surging from letting off the brakes.