You'd be better off if it was worse in the sunshine lately.
Connections to ECU and MAF etc might be getting damp and affecting signals. Unplug em all one by one re-plug un-plug a few times to clean up the contacts then apply some of that greasy stuff for electrical gizmos from Maplins. (Soz, can't remember what it's called but there's a thread about it here somewhere.)
Hope this helps.