I have been getting a small random misfire p0300 code. The CEL turns on and off throughout the day. When it reaches a 1/4 tank of gas, the misfire is gone and the car idles smooth. But as soon as I fill up the tank, idle is shaky and misfire p0300 is back. The car is Vortech supercharged.

 

Could be anything. Plugs, coilpacks, vaccuum leak, bad gasket.

Has it been tuned after the SC install?

 

New plugs, smoke test - no leak. It has been tuned a long time ago.

 

Is it filling up normally at the gas station or does it give you a hard time?

 

Fills up normally. It now shows the misfire code regardless of the fuel level. Sometimes when I drive the car, idle is stable. Other times it shakes between 800-850 rpm.

I cleaned the maf sensor because it was all oily and the AFR became leaner at idle.

The p0300 code jumps from pending (yellow code) to current fault (red).

 

Have you gone through while its happening and disconnected the coil packs 1 by 1 to see if there's an effect? Also could run it for a bit and pull the plugs to check for dampness. You could also try venting the evap canister to atmosphere and see if that makes any difference.

Been chasing down the same code on my car since I got it running, so just throwing out different things I've tried. Mine appears to be evap related but who knows if that will actually fix it. The p0300 has to be the worst, most generic, code ever. It sucks.

 

I disabled the cylinders one by one using a scan tool. They all made car very shaky.

Could blowby oil in the intake system cause p0300?

I have noticed when I changed my spark plugs, the cylinder 4 spark plug had a brown residue where the ignition coil boot seals the spark plug.

 

That's the rocker cover o-ring around the spark plug letting oil through onto the spark plug

 

If your talking about this it's pretty normal so have minor staining.

http://www.ngkntk.co.uk/index.php/te.../corono-stain/