EGR and braking

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Ive had a rough-idle/stall issue with my pickup (91 Chev K1500, 4.3, AT). Thought it was a vacuum leak. Replaced IAC valce, dist cap (badly corroded), rotor, plugs, wires. I also just replaced the EGR valve because when I sprayed carb cleaner near it, the engine revved. Since replacing the EGR valve, I experienced intermitten hard pedal. Could it be that my brake booster was the source of the vacuum leak? Why would it be affected by changing the EGR valve? Just coincidence?l

As a side note, Ive not ruled out intake gaskets yet. I am also replacing the throttle body gasket.
 
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It is always possible that when replacing all that you caused a leak by cracking a vacuum hose or connection. Lots of old brittle plastic under that hood by now. You may have a bad booster check valve. I would replace that cheap part before looking at the booster itself. They are not known to fail commonly, but on an older car I would look there first.
 
The brake booster vacuum source is "always on" while the EGR one gets ported. The two never mix and by design the brake booster vacuum is isolated from the rest of the system for safety.

The idea of a bad diaphragm makes sense. Even if you had a bad check valve the booster vacuum supply should charge up after about 3 seconds of running.
 
I just replaced the throttle body gasket. A much easier job than i had anticipated. I dont know yet if that was the source of my idle problem yet, too early to tell. But I took it on a hiway run and it seems to have tremendously more power and the throttle is much more rsponsive. I will look into replacing the booster check valve.
 
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