1999 Chevy Suburban K1500 LT
So a few days ago I went to start up my car and it was running about as good as a beached whale running a triathlon. So i used my code reader and got 2 P0300 codes which is random multiple misfire. I looked up the causes and parts that could fail (most of the parts on my engine are original) and came up with a few that were known to cause this issue. So I changed my spark plugs (on passenger side two had small carbon build up and were thrashed), replaced the fuel filter, ignition coil, ignition control module, ignition cables, made sure I was getting power from my distributor, and have checked every electrical connector and hose on my engine. Only things I haven't checked that are possible causes are the fuel injector unit (my engine uses the wonderful spider unit that is beloved by everyone) and the fuel pressure regulator. I have a feeling I'm not getting proper fuel pressure but I haven't been able to secure and pressure tester yet so that's next on the list. Also some side notes, the engine is supposed to idle around 810 rpms and currently idles around 700 and drops to 500 when put into gear. There is also a suspicious amount of liquid coming out of my exhaust but it doesn't have a smell to it. There's also the possibility of a vacuum leak so I'll be grabbing carb medic and testing around my engine for that. Any advice or previous experience with this I'd like to hear about.