My 97 GMC Suburban 5.7 that I just bought with 165,000 miles has had 3 different codes come up P0507,P0306 and P0300. I have only driven it about 400 miles and it has not lost any coolant but does appear to use some oil. When I first checked the plugs number 3,5 and 6 had a white ash fouling to them with 6 being the worst. I replaced plugs with some autolites I had and replaced cap and rotor which both had deposits on all the terminals inside the cap and on the rotor tip. I plugged all the holes on the valve covers and checked for suction on the dipstick tube which it did have. I was told this would mean it has an intake leak, But I also sprayed starting fluid around the edges of the intake but got no change in rpms. Before I get the gaskets and start tearing it apart is it possible that this random misfire and high idle are caused by a worn distributor gear or some other problem? Any advice is appreciated here.
Thanks,
ccnova

Welcome to AF. A lean condition can cause the symptoms also, I would check fuel pressure, the Vortec (I assume this is your engine?) needs 60-65 psi, pumps are weak in this truck as well as the FPR. Also would do a full scan and look at fuel trims and o2 sensor activity for a more thorough diagnosis. 507 can be caused by the iac or throttle body being carboned up or the throttle body shaft being worn allowing unmtered air into the engine.