Crazy high idle & EACV

[AZmike]

I have a high idle pretty much all the time: warm, cold, whenever. The idle never drops below about 1050 and sometimes stays as high as 2900 It seems to idle at a different speed at each traffic signal.

I know the EACV is letting in the air since the idle returns to the normal ~700 when I disconnect it. Of course this makes the computer unhappy and it switches on the check engine light. With the EACV disconnected if I give it throttle the engine speed will pulse +- about 200 rpm and run poorly, so going without the valve is not an option. I've removed the EACV cleaned it out thoroughly (it didn't look too bad inside) and reinstalled it with a new gasket--same problem, but at least the highest it got was 2200. I'm not sure if the EACV is the root cause of the problem or if something else is telling the ECU to let in more air. There are no codes from the ECU and the engine, ignition, and fuel systems are in good condition.

Can the EACV go bad and the ECU not notice? The internal resistance in within spec, there is battery voltage at the connector, and neither of the terminals is grounded. The next (and last) step in the factory service manual is to try a known good ECU. For what it's worth I had a code 12 a few months ago. Its run fine without a code since then after just shutting down and restarting it. I disconnected the EGR during some of my testing and it had no effect on idle.

I was hoping for some good input before going digging around at the junkyard and haggling for another EACV and ECU--if they're available. Opinions and suggestion appreciated.

[Strugglebucket]

it sounds like the eacv is still good. i've had high/pulsing idle problems before and unplugging the eacv would make it go away but it wasn't the cause of the problem.

are you sure you don't have a leak somewhere on the intake manifold? have you checked that the throttle closes all the way, all the time?

[88Accord-DX]

Sure you went over this (http://3geez.com/showthread.php?t=96).


The idle speed is controlled by three methods:

1.The cold idle valve, which is located under the throttle plate. The valve consists of a air channel bypassing the throttle plate which is blocked once coolant heats up a wax element. When the engine is cold the cold idle valve will allow a lot of air to bypass the throttle plate, and the idle will be around 2000 rpm. As the coolant warms up the cold idle valve will slowly close, bringing the idle speed down.

2. The idle air control valve (IAC or EACV), which is located on the back of the intake manifold. The IAC valve is a solenoid which is controlled by the ECU using pulse width modulation. Thus the ECU can control how far the solenoid is open and how much air bypasses the throttle plate. There are limits, both upper and lower, to the amount of air which passes through the valve because the solenoid will only work from 20% to 80% duty cycle.

3. The throttle air bypass screw, which is located in the top of the throttle body. Unscrewing this will allow more air to bypass the throttle plate, and so will increase the idle speed. The purpose of the bypass screw is to adjust the amount of air going pass the throttle plate so that the IAC valve duty cycle is within the limits of what the ECU can control. The manual tells you how to adjust this screw by unplugging the IAC valve.

A multimeter measing duty cycle would figure out this problem when connected to the EACV. If you don't seem to find the problem by adjusting the screw & uplugging the EACV, get one at the junkyard before you blame the ECU.

[AZmike]

Thanks for the replies.

The EACV troubleshooting guide on 3geez is straight out of the manual that I was using. I had already cleaned the throttle body but I went over it again with an old toothbrush and more cleaner. The throttle plate is closing all the way. With the EACV disconnected (closed) the idle is slightly lower than normal so I'm pretty confident I don't have a vacuum leak.

After resetting the computer a few times and adjusting the idle screw I've got it so it rarely gets over 1400 once warmed up, but it's stil not right. I'll try another EACV from the junkyard and start testing individual sensors if that doesn't correct things. Hopefully I don't need to get a new valve from the dealer since they're $150+.

[Morthane]

I had a bit of this prob, I had to replace a thermovalve I think... again, I'm no expert :ugh: