I have a Honda Civic LX 95. I gotten a IACV and tested it. Used volt and ohm test and passed. When turn key on there is power to the IACV and it clicks. When cold and started there is power (meter tested also). Have a little idle up & down for a short time then gone. But when normal operating temperature, disconnect the IACV no idle drop and no power at the connecter only when key is on (not started). When turning on AC also no power, engine idles low. What gives it power or is there a relay that’s not working. Hope it is not the computer.

 

One wire should always be live (battery voltage) whenever the key is on. I think it is teed into the main black and yellow wire circuit that runs the alternator, distributor, VSS, canister purge valve, etc. The ECU drives the other wire to ground to open the valve.

 

Well, see the problem is when the engine is cold and you start it there in power to the IACV for a little while, then no more power to the IACV. One of the test to the IACV is also to wait till normal operating temperature and after the fan go’s off, to disconnect the connecter to the IACV and the idle suppose to drop. So I thought my IACV was not working, but finding out that there is no power at the connecter. There should be power but I don’t know why there isn’t when at normal operating temperature. I could turn the key and there is power but when starting the motor at normal operating temperature no power. Why there is no power there? What supposed to gives it power? A sensor? A Relay?

 

If you have zero volts from either wire to ground, and everything else on the car works, seems there must be a defect in the engine harness itself. I think there are internal connections to the other things I mentioned. All of that is powered up from the key switch and a fuse under the dash. If you did lose the whole circuit though, other things would not work either. See if you have power on the "I" wire at the alternator when the IACV does not have power.

 

The Yel/Blk wire gets voltage from the main relay. Upstream of the IACV connector (red highlighted), scrape away a small amount of wire insulation to check for voltage to body ground with and without the engine running. If you now measure voltage under both conditions, the IACV plug itself may be the problem.

 

Ok, I will check that.

 

This diagram helped me alot. I have not tested anything yet. But I could see how it is inter connected. Thanks, I will let you know what happen.

 

Hay, Ron. For two years I had this problem. Everybody guessed this and that. It was like that since I had the car. This diagram, think I found the problem. Trace the wires. The only thing I need to make sure 1) Does power should be always at the connecter to the IACV, at all times? The reason I ask is that, I believe that that the IACV connecter and the EVAP were switched. These connecters works on ether or. Interchangeable. The connecter on that was on EVAP, has constint power (when motoris running). But the wire has Light blue/White , diagram shows GRN/WHT (with YEL/BLK). Don’t know if this maters. The connecter that was on the IACV s the wire is a solid red (with YEL/BLK) and only has power when it is cold. I believe they were swopped at one time. Just need the color code of the wire to the EVAP, is it a solid color (with YEL/BLK)?

 

The "Purge Cutoff Solenoid" is the EVAP valve. So plug with solid red wire should go there.

All the yellow/black wires should be live (battery voltage measured from the wire to ground) whenever the engine is running.

 

What mk says here is backed up by the circuit diagram. The Yel/Blk wires should be hot with the engine running or with the key in ON(II) without the engine running.

Plug the connector with the red wire into the EVAP solenoid and plug the connector with the Lt Blu/Wht wire into the IACV to see if the idle problem is fixed. The green in the Grn/Wht wire has likely faded over time to have a Lt Blu appearance.