High revs

I posted this message a while back. Someone please help. My 94 Ford Escort 1.9L is still revving high on initial start up. I know this is normal, but why should it take 5 minutes be fore the tach drops down to 900 prms? I changed the Idle Air Control valve- nochange. The car never over heats or anything. Went throught the entire summer without it reaching to the half mark on the engine temp insdicator. Someone recommemded the PCV valve? I dunno.
P.S I have a cold air intake., Don't know if that info will help.

Cold air intake may be a cause.
Check in to the Engine Coolant Temp switch near the thermostat. It sends the temp to the computer which is responsible for controlling the mix of things. The other sensor goes direct to the gauge. The sensor closest to the thermostat is the one to check. If it is faulty, that could be part of what is taking longer.