I drive a stock 99 DX civic. Its my daily. My CEL started flashing on my dash about a week ago. Ran OBD2, got codes p0300, p0301, p0303 and p0304.
Listed below is what ive done to try and fix the misfires. Car still turns over fine, doesnt stall either. Only has a hard time accelerating from a stop and idles rough. When pulled old plugs there was a lot of carbon build up for them being only 2 yrs old.

New plugs gapped at following
​​​​​.041 .040 .041 .041
New spark plug wires
New cap and rotor
No milky oil
No excessive white smoke from exhaust
Normal clear anti freeze
Fuel filter replaced this yr march
Air filter replaced last yr October
Compression test. Results listed (No lost of compression) C1=170 C2=165 C3=180 C4=180
Cat and exhaust mainfold replaced this yr march dur to a crack in manifold leading to a vacuum behind the heat sheild.
"New distributor" from junk yard
Sprayed wires with water at night. (Saw no arc between wires).
Sprayed carb cleaner on cold engine near intake manifold, fuel lines and air intake. (No change in rpm).
Checked all fuel injectors with multimeter and screwdriver to ear. (All right ohms and heard rhythmic ticking in all)


Next was going to unplug sensors controling air intake readings. Any other suggestion? Ive tried so much and nothing is coming up.

 

[QUOTE=ArmyOfMany;52777343]I drive a stock 99 DX civic. Its my daily. My CEL started flashing on my dash about a week ago. Ran OBD2, got codes p0300, p0301, p0303 and p0304.
Listed below is what ive done to try and fix the misfires. Car still turns over fine, doesnt stall either. Only has a hard time accelerating from a stop and idles rough. When pulled old plugs there was a lot of carbon build up for them being only 2 yrs old.

New plugs gapped at following
​​​​​.041 .040 .041 .041
New spark plug wires
New cap and rotor
No milky oil
No excessive white smoke from exhaust
Normal clear anti freeze
Fuel filter replaced this yr march
Air filter replaced last yr October
Compression test. Results listed (No lost of compression) C1=170 C2=165 C3=180 C4=180
Cat and exhaust mainfold replaced this yr march dur to a crack in manifold leading to a vacuum behind the heat sheild.
"New distributor" from junk yard
Sprayed wires with water at night. (Saw no arc between wires).
Sprayed carb cleaner on cold engine near intake manifold, fuel lines and air intake. (No change in rpm).
Checked all fuel injectors with multimeter and screwdriver to ear. (All right ohms and heard rhythmic ticking in all)


PO300/1399 fix 2000 civic ex - Honda-Tech - Honda Forum Discussion

 

PO300/1399 fix 2000 civic ex - Honda-Tech - Honda Forum Discussion[/QUOTE]

Thank you! Did not see this post while I was searching "P0300". I will take a look into it and try to clean out my throttle body today if it does rain.