OK i have a 95 civic ex. When you start up the car it revs up to 3k then drops to 1500. then revs back up to 3k and it does it over and over again untill the car is warmed up. What could be causeing this?

 

Sounds like a vacuum leak or possibly the IACV.

 

Check for coolant level , Make sure you have coolant in your cooling system . Alot of Honda-Acura enthusist have this similar problem and usually its a low coolant level so be aware & make sure you fill that baby up ... GOOD LUCK

 

LOL, my buddy had this same prob on his project...
He had gotten a 93 DX hatch shell and we put in a B16A2, he had the EXACT same problem, we couldn't figure it out for like 2 months...
Turns out it wasn't a vacuum hose leak, but the seal around the brake booster (large circular thing in front of driver side on firewall) was bad, causing air to get in and cause the crazy idle...
Some glue/caulking fixed it right up!
Hope this helps I know it took us a LONG time cause we thought it was an actual vac hose leaking...

 

spray brakeleen alove the hoses on your motor it should help u isolate the problem

 

you need coolant and you probably have a leak in one of your EACH hoses or thermo valve hoses, Ive had this problem many of times trust me on this, just pop the cap on the radiator and fill the radiator to the brim then squeeze the top radiator hose till it pushes air out and sucks more coolant in once you have filled the radiator to the top and can't get anymore air out of it just put the cap back on.

If that wasn't the problem then my next question is did you put on an extra IAB manifold, the 1 inch thick piece that bolts on inbetween the plenium and the manifold because that mod caused that problem for me as well no matter how sealed I made it. if thats not the case then it has to be a vacuum leak or a hose popped off of your manifold letting your manifold suck freely.

 

Where is this guy Pinkys?

I wonder if he ever fixed his problem...

 

BUMP Same problem (D15B7 though) but my idle range is more like 0-1000 RPM.

EDIT: The idle problem is fairly inconsistent, but bringing the engine up to operating temp doesn't seem to help.

 

If the range is drastick like 0-3000, then you need coolant for sure or you have a coolant leak somewhere within your EACV valve and your Thermovalve, check those hoses, I know on my 94' Prelude there are 4 hoses between the two components.

Just remove the cap on top of the radiator "not the overflow tank cap". Pour in radiator coolant and squeeze upper radiator hose to push the air out of the radiator, keep doing that till you can't force anymore air bubbles out of the coolant system to suck down anymore of the coolant you are trying to add, then simply tighten the radiator cap back on and start up the car should be good again.

If the range is little, such as 0-1300 rpm's, then simply check your oil "make sure you do the check when the engine is cold" If you try to check it right after you ran the car, the oil will be hot and read incorrectly telling you that you have somewhere around a 1/2 a quart more than you really do. If you had enough oil then check your idle screw, try turning it to the right till your rpm's drop, but if you get to the end and it is still doing this small rev, then you could have advanced timing, one of your accessory belts could be either far too tight or even a little bit too loose, your throttle cable could need adjustment or replacement "if there are any extreme bends or kinks in the cable you need to have it replaced. There could be a small vacuum leak somewhere around your intake manifold, and there are another very rare instances that it could be but I would start with all of those first, then if that doesn't fix the problem just let me know and ill be sure to try to help ya out. Anyways goodluck guys I know how annoying the sound of engine hi-rev is but with patience and a little adjustment it will go away.