idling problem

[arf4n]

so i fitted a b18c4 along with a s21 gearbox but the are a few problems;

1) when starting up cold, the revs sit at just under 1k. Isnt it meant to be higher when cold - what the fitv does? but the engine doesnt have a fitv

2) when starting up warm, the revs jump between 300 to 700, so not they're not consistant

3) sometimes when pulling up and/or slowing for a junction it just turns completely off

4) oil pressure light stays on but goes off when i give it a slight rev, could this be because of using a D16Z6 vtec solenoid?

i have cleaned out the iacv but didnt help