Ok, especially during the colder months I have trouble stating my rex. It will "miss-fire" and make an ugly scratching/rattlingnoise from the engine bay.

When it happens I turn the car off and restart it holding it longer in accessories so things get power etc and after a couple of goes it works. I thing idle the car to get it warmed up
This happens a lot more during the cooler months! I don’t know what’s causing it and I’m not sure if the alarm system I got fitted has anything to do with it.

Does anyone think it maybe the ignition wires under the bonnet getting cold/residue on it? I'll retape tonight, see if it makes any difference

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Classic WRX = Best

After Market Fuel pump at all?

What mods have you got on your car.
I get a similar thing but I have a MoTeC and we are still sorting the Intake Air Temp. compensation maps.

Once the car warms up it's fine, just when it's cold, feels sluggish and pops back through the intake. Does this sound like what's happening to you?

after replacing the rocker covers a few months back i always warm up my car and then drive it casually for ages before 'giving it shit' even more so durng these cooler months (drive to work 6am-7amish)

its not really sluggish, its acutally quite the opposite when its cold
fucking thing flies!! im not sure whats causing your problems but as you said prolly to do with the mapping

not sure about the fuel pump whats a stock one look like?

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Classic WRX = Best

do u have a aftermarket ecu? i have a link and when it started getting colder in the mornings my car could not start for a couple of goes, so i got rms to adjust the cold start on the ecu. works fine now