i absolute need some help, i don't have much experience i've been having my grandpa help me replace my valve covers. we did that & had a bunch of codes pop up we eventually got most of them taken care of but the only code that's now popping up is that p0300 random misfire we thought it would've been a vacuum leak sprayed some WD-40 around the engine my idle stayed on 1000 rpm. we thought it then could've been a fuel pressure problem so we pulled the fuel fuse and the car died automatically we then change the fuel pump, fuel injectors twice and still the same results we tried the ecu relearn & still nothing at this point i'm lost.

 

Sure you didn't mix up the coil pack harnesses? It's really easy to do.

It's also easy to pinch the oil fill neck between the upper and lower intake plenums.

Any time you unplug the throttle body you need to recalibrate the throttlec closedpositionand also the idle air volume relearn.

Section EC - Engine Controls in the FSM, it's at the front under "basic service procedures".

 

Also, P0300 has absolutely nothing to do with a vacuum leak. That code means there is a misfire but the ECM is still detecting all coil packs functioning. It's very possible to mix up the coil pack harnesses and get two of them swapped, this throws the combustion timing off and will cause that code.

 

Your high idle is probably because you disconnected a bunch of stuff and didn't do the relearns, I would troubleshoot this as unrelated to the misfire. Also, manually working the throttle butterfly valve by hand is commonly known to break the throttle motor, if it was opened up manually for cleaning there's a good chance it's damaged.

 

How bad is the misfire? Is it bad enough where the car is almost not driveable?

 

I agree with cleric670. Check the coil pair wires on the drivers side. cylinder 4 and 6 tend to get mixed up(middle and coil closest to firewall). Cylinder 4 (middle) has 1 grey solid wire while cylinder 6 should have a grey.red wire.

here's the cylinder layout for a more clear pic!

 

Could the mass flow air sensor be the reason for a P0300 code?failed my damn state inspection.

 

so wait? you failed the state inspection because of the p0300? or you have the mass airflow code and the p0300 code and wonder if they are related?

 

As far as I know, most any states that have inspection if you have any CEL code you automatically fail. CA and NY are the worst.
A dirty or damaged MAF can create a misfire. You can try cleaning it with MAF spray, but I would check for vacuum leaks as well. Intake boots are common to crack.