I have a 94 civic ex with the d16z6
Every morning I start my car it idle between 2000-2500 rpms. What could cause this.
Also when I press on the gas after shifting I can hear a whistle/hissing sound

 

Since when?
Clean IACV & FITV.

 

air leak? check your hoses, the throttle body gasket and IM gasket.

do you have an aftermarket intake? if so, that could be the hissing/whistle your hearing....

after it warms up where is the idle at?

and like grumblemarc said, your fitv could need adjusting.

 

I have an aftermarket intake and that hissing sound is from the intake dont worry. Clean/ adjust the fitv and report back.

 

i am having the same problem with the b18c with type-r head in my eg..it doesnt do it all the time..only cold when i start it(3000) RPM...and while sitting..

 

Yes I do have a aftermarket intake..but the whistle noise is not from that cause I put the stock intake back on the see if it made the whistle noise and it did.

After a minute or so it idles it 500 rpms

 

sounds like a simple fitv adjustment and cleaning like everybody else said.........
Also there is a little breather on the transmission and when you clutch in it pushes air out of it making a whistling noise.

 

Definitely iacv/ fitv related. Should idle at/around 1700-2000 on first startup and calm down to 750-900 after at operating temperature