Cylinder not firing on startup

[domV8]

When I start the car up from cold, it seems that (at least) 1 of the cylinders isn't firing initially - car vibrates very slightly (normally smooth) and there is the occasional (almost unnoticeable) jolt on acceleration.

Goes after about a minute, back to its normal smooth self.

Car runs aftermarket ECU with coilpacks - not had any problems for 3-odd years, just started happening.

Any ideas on common causes for this? My complete guesses might be..:

- dodgy sparkplug
- HT lead issue
- sticky valve
- lifter taking time to pump up (but no tapping sound?)
- injector issue
.......

The crux of it it that it resolves itself within a minute - might indicate something to those with more technical knowledge than I...

Unfortunately don't have any tools to test things etc, so trying to eliminate/pinpoint causes via theory at the moment...

Thanks,


Dom