So a little back story on this car, I bought it for cheap and the guy said it just needed a head gasket since oil was mixing with the coolant.

Ordered a head gasket (and timing belt set while I was at it) and just got it all put together today and I'm having some problems

It's overheating after idling for about 10 minutes, the fans seem late to kick on if at all, I don't know if it was me fiddling with the AC that was starting the fans or if it was temperature activated.

And it doesn't want to rev very high. I didn't push it but I couldn't get it to stay at 4k rpms. It'll go up to 4k, drop to 2k, jump somewhere to 3.5k, drop again, jump up to 4k once more. Over and over again. Could I have forgotten to plug something in?

So my problems are the overheating and the idling problem. I replaced the water pump so it's not that. The radiator looks to be fairly new, the fins aren't bent and I can run water through it with the garden hose. The rad hoses aren't clogged, and the thermostat is brand new.

any ideas?

 

Did you test before pulling the head?
Did you have the block and head checked for straightness?
Did you bleed the cooling system after refilling?

 

if all you did was replace the gasket without having the head resurfaced then its time to pull the head and do it right