Re: EGR valve problem????
P0300 indicates misfire, I'd pull the plugs and inspect the wires. If they've got some time on them, might as well replace them.
The EGR, if the engine was running, yes, there should be vacuum. You might might want to replace your vacuum lines as well, including the bushing for the PCV. However, that low of a vacuum should throw a code as well. Best thing prior to getting too hairy with replacements, check running vacuum at idle.
Prius repellant, just add gas.