My short term trim per UG bounces around from -5 to +5. I noticed while sitting at a light and pumping the brake pedal makes it go up as high as +15.

Normal? No? Kind of an odd scenario and not a normal test but can anyone shed any light?

 

Not sure if it's normal. My engine is all over the garage right now. But possible vacuum leak? Maybe inspect the booster and vacuum lines? They are starting to get older for all of our cars. Does anyone know where to replace the plastic vacuum lines by the way?

 

Yes, brake booster indicates you have a vacuum leak somewhere. You can hook up a shop vac to the intake pipe and it will whistle at the leak.