Holden Commodore: Backfiring issues

My VT Series 2 V6 Commodore has an intermittent miss. No error codes are coming up, and I have replaced the plugs, leads, coil packs and DFI, and cleaned all the connectors on MAF, TPS, IAC, and CAS. I have also checked the purge valve and hoses for vacuum leaks, cleaned the injectors with a treatment and checked the temp sensor for accuracy. The misfire occurs mostly when cold, and it will occasionally stall at idle, for about the first 20 minutes of a drive. It stalls maybe three times in 20 minutes; there could be a heavy misfire from idle for three seconds, clearing as you accelerate, and the odd single misfire. I can rule out the CAS ? if that were misbehaving it wouldn't run at all. The misfire was a sudden onset thing, so I suspect it?s a failure rather than a wear-out situation. The only thing that I can think of is a transient blockage in the fuel line or a bung injector that works ok when hot. Any thoughts?