mattcod6fan

I have been having idle problems with my 1988 honda civic d15b2. After searching the internet I read that the most common cause of this was the IACV. But a new IACV for my car is $230 and I could not find a way to test if it was for sure the IACV or something else. So i decided to share a sure way of knowing whether you have a bad IACV or if the problem is something else.

The idle air control valve or IACV adjust the idle of your engine based on the amount of air that is going into the engine and the temperature of your coolant. The first thing you should do is make sure that your car's coolant has been bled and that their is no air in the cooling system. This can cause the IACV to get an inaccurate temperature reading and cause false symptoms of a bad IACV.

Next, you will need to get your engine to a normal operating temperature. To do this, turn the car on, in nuetral and keep the rpms at around 2k until the radiator fans turn on. Now to test if the IACV is closing all the way like it should, turn the car off and take off the IACV. Cover the two holes on the bottom with a piece of tape so that no air can travel through the holes and reinstall the IACV. Turn the car back on, if the car idles normal then you know that the IACV is not closing all the way. Check the wires and plug going into the IACV and clean/replace the IACV.

To test if the the valve is stuck shut or not opening, you will have to ground one of the wires going into the IACV while the car is on. To figure out which wire to ground, use an ohmmeter. One wire should have a constant voltage and one should have a voltage that is constantly changing. The one that is constantly changing is the one you need to ground. If the rpms increase when it is grounded, then the IACV is opening. If not, clean/replace the IACV.

Hope this helps.

95gsr@530

Quick check for power/continuity to the IACV; KOEO available voltage at yellow black wire should be battery voltage. This is out of Chilton for my 95 gsr. Jumping the valve to battery voltage should induce a click. Tape over the air bypass ports sounds a little sketchy, but in theory, should work as a test. Another diagnostic step Chilton spells out for my GSR is reaching op temp (radiator fan cycles) and disconnecting connector to IACV. A decrease in RPM, or stall, would indicate faulty valve. And again this is just for the 2 wire type, which is used for both OBD1 and OBD2 applications.

FlewByU352

I don't understand the tape method. If you are blocking the holes or have the IACV disconnected, the idle should drop which indicated the IACV is working. If it doesn't drop, you either have a vacuum leak or your throttle plate has been adjusted to idle without the IACV.

Caoboy

If the idle doesn't drop with the tape or your finger covering the top hole of the TB, then it indicates the IACV is not working.

Does this make sense?

FlewByU352

Don't you think that this is a pointless test? There is nothing measured by data or numbers. I've had bad IACV's that still open and close but are slow to react much like an old O2 sensor. Sure it reacts, but not fast enough to be considered good.

Caoboy

Mainly it's a quick test to show if it is working or not, rather than seeing how fast it is working.

I understand what you mean by a lazy IACV...I had one that would occasionally stick, I had to take it apart and clean it (newer 1996 throttlebody version)

FlewByU352

Something to be noted is the non-vtec B series IACV have a 5/16" opening and the VTEC are 1/2". I've drilled out the non VTEC to around 7/16" as the wall is thinner before hitting the o-ring gasket. I believe the internals are different as well but I've never compared.

F22Master

Also, the IACV does NOT, in any way, measure the temperature of the coolant flowing through it. Plenty of people, including myself, have rerouted our coolant lines so that they no longer go through the IACV, and it still works just fine.

Just to clear things up.