2000 Chevy Blazer 4WD 4.3. The car has codes p0302 and p0456. I have been having issues with this car for some time. Rough idle and smell raw gas out of the exhaust. Recently replaced coil, distributor cap and rotor button, upper and lower intake gasket, spark plugs and wires, and regulator. All AC Delco parts but the regulator. I also took the spider injectors apart and cleaned thoroughly. I did a vacuum test and have 16 on start-up and then when snap throttle, it goes to zero and stays there. I thought it might be a clogged catalytic converter so I took out the front O2 sensor but no difference. Does anyone have any information on what this could possibly be? Help is greatly appreciated.
Thanks, Kenny

 

I have the same rig. I would highly recommend checking all the vacuum tubing for rotting, and check the 4x4 actuator under the battery tray to see if it's rubber diaphram is intact.

 

After reading your reply and checking things out, I discovered my 4WD is not working either. The 4x4 actuator appears to be intact. I also checked the vacuum switching solenoid valve. If I blow into the top air line under the wiring harness connector air will come the small hole on the top. Is this correct or should it be closed system? Since I am pulling the p0456 code, do you think these symptoms could be from the canister/EVAP purge valve? Thanks so much man.

 

If you have the 4-button controlled 4wd system, check out the thread I maintain about replacing the engine compartment vacuum hoses. The link is below in my signature.

From what you wrote, it sounds like you have a vacuum solenoid in the engine compartment hanging from the rim of the sheet-metal at the center/top of the firewall? To work properly, that valve must vent to atmosphere so that the diaphragm that pulls on the front axle cable can return to its neutral position. All of the underhood vacuum hoses are susceptible to rot or being worn through. It is well worth replacing all of them.

Because the HVAC system is also vacuum actuated, problems with vacuum will also affect how it works. The symptoms include air of the wrong temperature being delivered and/or the air being delivered to the wrong vent.