Ok so Im posting for a friend. He has a 93 civic ex with the d16 vtech. He has a problem with his car idling. When at idle it will rev form 1 to 2k rpms back and forth over and over again. It does it when the clutch is enguaged when driving also. Does it when it is warm and cold. He has taken to a couple of local mechanics and they all said it was the IAC vavle. He replaced that and it still has the same problem. Any help would this would be greatly appriciated.

 

Clean and adjust the FITV on the throttle body:

http://www.honda-tech.com/showthread.php?t=1564019

 

First make sure the throttle cable goes slack and the throttle plate closes completely when not pressing the gas pedal.

If you take the intake hose from the air cleaner off at the throttle body, you will see holes in the side of the throttle body before the throttle plate. These bring air into the engine when idling. The one on the back goes to the IACV, the one on the bottom to the FITV, and the one on top to the air screw. Start the engine and block them with your finger to see which ones are pulling air. When the engine is warm and idling too fast, the FITV and IACV should not be flowing. If you block all the holes the engine should stall. If it doesn't there is air getting in somewhere else, such as a bad gasket or the brake booster or other vacuum device. Air entering the manifold from anywhere will increase the idle speed.