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Couple of things. I have a 1979 Pontiac Firebird with a 3.8 liter v6 231 cid. This car was built in Van Nuys and has the california Emissions High altitude Non Air system in it. I am having running issues. The car runs fine then suddenly cuts out or bogs immediately at times when throttle is hit. This problem is intermittent and all fuel system items have been replaced from tank to carb. I am currently attempting to rebuild the emissions system in hopes that it could be the failure. However I have run into the problem of not being able to locat parts needed. Mainly my issue lyes in 2 parts The Distributor System/ Vacuum Modulator Valve (DS/ VMV) PN- 560694 and the Thermal Vacuum switch 3 Port intake mounted PN-3042272. I found a matching PN to 560694 through autozone however it was to a 2 port intake mounting thermal vacuum swithch and the DS/VMV of which i speak is a free floating cylindrical valve with three ports which sits on the drivers side bank of intake between the carb and valve covers. Any advice or tricks would be helpfull. Thx.
 

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Both GM part# you listed are discontinued...

#560594 can be procured through VPI, your local GM dealer should be able to help you with that one...

The other#, 1 GM dealer in Arizona lists...beyond that...you are SOL I'm afraid.

You could try a real parts store like NAPA or CarQuest that might have a OEM crossover...
 

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Where did you get the carb? Make sure it isn't leaking and that the accelerator pump is working. If your EGR valve is sticking, it'll run really badly and that may be the issue. Check your state laws about emissions sytems and obsolete parts. Many areas have exceptions when emissions parts are no longer available. My advice would be to scrap the high-altitude spark control and change to a 49state thermal vacuum switch to control the EGR.
Clean it and make sure the valve is moving properly and advance the distributor to match. Generally speaking if the engine is in good condition a 2-gas test is pretty easy to pass, especially with a modern catalytic converter.
 
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