G'day! Did a search on this site and perhaps confirmed what I believe to be the problem with my unit. Symptoms:excessive hissing when brake pedal applied and held,also longer pedal travel,almost immediate loss of vac assist after motor shut down and still rolling. Some earlier threads I saw IAC issues as a possibility,but as I cleaned mine less than a year ago and am also experiencing some erratic idle (warm) I am leaning towards the booster as the issue.Will test check valve and lines when its light.But this would explain my idle issue if the booster is shot! NEVER have had to replace one on any vehicle! Seems very strait forward,but from what I am reading people can't access the inner nuts(huh?) and also can't remove the clip from the pedal linkage to the thrust rod(again,huh?) It seems one doesn't even have to drop any dash panels...but! Does that clip break easily? Are they readily available? Thanks for any input!
Specs are 97 Jimmy, W 4.3 JM3 brake system.

 

the bolts and clip and all that are pretty easy to get at unless you are a very large individual. you just have to lay on your driverside floor and get them from under the dash. sometimes there will be insilation or like cardboard type material in the way just move it or remove it to get at the bolts. so its basically a clip, slide the rod off, then 4 or 6 bolts and it comes off.

dont take the lines off the master cylinder, just unbolt it and move it away a bit, maybe hang it with a bungee cord.

just make sure you dont just have a major leak somewhere else causing the booster to lose pressure, but if its hissing when you push the pedal thats probably your problem

 

The job looks like 45 minutes maybene of the easier dash component R & R unit on this car! Theres no other vac leaks evident. A bungie is always ready for this type of stuff,I wasn't cracking the hyd system...
maybe I'll get to this mid-week...

 

even quicker if you have access to air tools. those nuts are usually lock nuts so ratcheting them off is kinda slow by hand