Hey everyone. I am an electrical engineer and have an idea on how to create a divice that will keep the idle stable by bypassing the ecu control. I just got a '99 Civic Coupe EX and have the up and down, high (about 1500rpm most of the time) idlle problem. what this device will do is, it will control the IACV and it will be adjustable by having two push buttons. The connection will be made by using the ECU Pin diagram. It will take five wire connections, 3 for power and 2 for the IACV. I will be building a prototype to test on my car very soon. After testing and making sure it is safe to use, I will be building more and sell them on ebay. An estimate of the price will be from $30 to $50 depending on the final list of parts. What do you guys think? and of course mad discount for HCF members. Also, if you have any comments on how I can make this idea better, I would appreciate it. Thanks.

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How well do you understand the system? I haven't looked into it much, but I would be willing to help. I do have electrical/electronics knowledge.

 

My understanding is that the IACV is controlled by pulse modulation. With a Scope I can measure the frequency of the pulse and with a microcontroller I can recreate it and make it adjustable.

 

Pulse width modulation(PWM) would be pretty simple to recreate and control, but what I would be more concerned about is the way the ECU will interpret the opening of a closed loop system. I assume it monitors the idle RPM and attempts to maintain a steady nominal value. In doing such if the end user is just a little bit off from what the ECU wants as a nominal value it will tend to drive it hard to the other extreme. This will most likely set off a malfunction code, however I haven’t really looked into it like I mentioned so I may be wrong.

 

Do we know for sure that the ECU monitors the RPM value?. I've been thinking that it doesn't make sense to monitor if it cannot adjust it and keep it steady at the correct RPM. Well, I will go ahead and try it. See what happens. Does anyone knows what interface we have from the ECU to the injectors?

 

to the injectors it used PWM and that I know is truly a closed loop system using the O2 sensor as the monitoring point. As for the RPM monitoring,.. I don't know for sure, but I do believe when you disconnect the idle control valve it will set off a CEL. I'll check this weekend.

 

Oh and when people say they have an up and down idle I interpret that as an under-damped closed loop control system. That is why I though the RPMs are being monitored and the control system may not be compensating properly and oscillating instead of maintaining a steady RPM.

 

Great info 97CivicEX. I firmly believe we are getting somewhere. If it's underdamped, the compensation must be corrected. If I just new what controls and what is used in compensation in terms of sensors and their voltages, may have a better understanding of this closed loop system. That way, I would just need to go back to my control systems book and review it to see what can be done.

 

Why is your idle not stable? Ive never heard of that happeneing unless something is wrong, ie a vacuum leak.


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That is my understanding as well. A vaccum leak would cause an imbalance in the air/fuel mixture or controls to the air fuel mixture causeing the oscillation I mentioned.