I've got a rebuilt streetported engine that misfires at idle (800rpm) after warmup.
I run stock ECU (J-spec FD), no mods, new spark plug wires, NGK BUR9EQP both leading and trailing. I've changed spark plugs, but it still misfires. Lambda is 0.7, HC and CO sky high.

Movie clip.

Old plugs.

New plugs, Leading, front to the left.

New plugs, Trailing, front to the left.

 

Is it missing or backfiring?

If it's missing you could need a new fuel filter or fuel pump.

If it's backfiring it could be a thousand things, like exhaust leak or running way too rich.