My_EFsedan

my brothers friend brought over a 99 civic si that he's owned brand new. car sounds like its misfiring when i first drove it. then notice the clutch is pretty much gone.

i replaced the clutch with a new set and feels much better. but still concerned about the misfire sound (like if it was running 3 or 2 cylinder).

use my obd2 scanner and shows:

p0300 - random misfire
p0302 - cylinder 2 misfire
p0304 - cylinder 4 misfire
p0113 - intake air temperature
p1399 - random/multiple misfire

read online of alot of possibilities of the causing of code p1399. i honestly done know where to start. after reading a few, i tried to do what i can with what i have.

so i changed (all new parts) spark plugs, wires cap and rotor. reset the codes. still the codes. changed the coil pack with a known working from my dizzy i bought new 2 years ago (sat a year after i blew my motor) reset codes and now only p0113 and p1399

the iat isnt a problem to me, but what can i do to fix the misfire code p1399?

any help is appreciated. tia.