SalsaGuy

So my son's 00 Civic EX, with 190+ miles, had the above codes. After wasting a hour on this forum chasing down a possible EGR issue, we went back to the basics. Having replaced the distributor/rotor/cap/plugs in the past year we used the Honda Shop Manual troubling shooting matrix, which by the way makes NO mention of the P1399. #1 cause for the P030X codes was Plug Wires (Only miss firing during accelerating). Although the wires looked in good shape, however being at least 6 y/o and aftermarket, they were replaced. That fixed the issue and no codes.

Still, after research, not sure what the P1399 is.

agb22

P1399 Random Cylinder Misfire

Clogged EGR passages can cause this code. You might want to check those first since it's easy. You just need to remove the upper intake cover and check the 6 ports under it. Clean the underside of that cover as well. As for the gaskets, they're steel and don't often require replacement. If you end up doing the valve adjustment, be very careful. If you get the valves too tight it can burn them up.