Bit of a weird one

Recently finished off doing an oil pump change, started up first time with good oil pressure, weird thing is my car ain't idling properly, it starts up ok, the revs drop to about 900rpm and then sounds like it's miss firing and the throttle response has gone slow.
My battery which is in the boot reads 14.45v but my spa gauge reads between 13.5-13.7, why would I have 2 different readings, I checked my grounds and plugs and nothing pops out at me, my car idles perfect when I disconnect my maf and revs up with good throttle response, car ran fine before the oil pump change

Total guess here damp in maf or oil vapours have covered the maff take it off clean it try that. Did you do anything with say a oil catch can or anything ? Clean the maff

Will do mate and I did disconnect the pipes to the oil can but that's about it, I'll give it a clean today after work and see if that helps

U ok with cleaning it what do you use ?

Just going to use a cotton bud and carb cleaner, see how that works out