2000 Honda Civic EXCodes P0300 - p0304 and P0118. Misfires under high load of low rpm
 

So on my 2000 civic I began noticing it was idling weird and having power issues under low RPM and high load. The Check engine light came on and was flashing so when I got it back home I checked the codes and got P0300 - P0304, which is a misfire for all cylinders plus another code for random misfire. There's also a P0118 code which is for the engine coolant temperature sensor. More than likely i'll have to replace this sensor but not so sure it's related to the misfire issue. Some background on the civic, I recently replaced the head about two months ago and did a valve adjustment, new belts, timing done correctly, new spark plugs and a new distributor. I checked for any leaks around the intake manifold gaskets and the exhaust manifold gaskets as well as the catalytic converter but didn't find any. I'm sure there's more possible vaccum leaks that could cause the misfire issue so can anyone suggest other places to check for vaccum leaks? I also read that the MAP sensor could be bad but i'm not getting any code on the map sensor for sending incorrect voltage and after unplugging it the car just about died. I'm sure it's doing something but plan to buy a new one anyways since there cheap and see how that works. I've heard some people mention that it could be a bad fuel pump or fuel filter? I could see the fuel pump being an issue but how about the fuel filter? I'm posting here hoping to get some more ideas of what else to check next that could cause the issue or if anyone has had a similar experience with misfires specifically under load at low RPM ranges? let me know if you would like or need more information. I'll post here to give an update on the MAP sensor, Engine coolant temperature sensor and fuel pressure tests. Thanks!