I got a bad misfire, stumbled really bad the other day to where I couldn't get it on the highway. It would backfire and stumble at idle and every single rpm.

I changed the plugs and it runs smoother, but at very very low rpm when I start to accelerate and also around 2400 rpm it stumbles but if I keep going it clears up.

So I went and changed out the rotor and cap since they were atleast 3 years old and it still does the same thing.

Fuel filter is 3 years old also.

Any other ideas on what it may be?

 

Still throwing P1399? Any other CEL codes?

You may also want to replace the plug wires.

 

I'm showing a "pending" p1339, since it only misfires for a little when I drive at certain rpms, it's not enough misfires in a row to throw the CEL light though