I have been explain to a mate of mine via email about adjusting the idle on my car (d16z6 civic) with the screw on the throttle body. He does not belive me cos his BMW has a stepper motor to control the idle which you cant adjust. Here is how i explained it, may not be right:

So what is the stepper motor connected to if it is the butterfly flap then it is different then mine cos mine has i Map sensor as i have explained what it does and a TPS senser(throttle position sensor) which is connected direct to butterfly flap. This sensor just tells the ecu what position the throttle is at. So between those two sensors and the Ecu that is all the control needed. there is a small drilling or tunnel that goes from about 20mm in front of the butterfly flap into the side of the throttle body and then surface behind the flat. The idle screw is like a tap on the drilling it adjusts the orifice size and so the amount of air entering the engine when throttle closed

i was alright at that point then he asked me:+

I see what you are saying, so how come your car doesnt stall when you are at idle
and you turn the stereo and heated window and full beam on?

Not sure on this one can someone help me. i know there is a idle control valve on the back of inlet manifold not sure what it does and how.

Can someone help me understand it please?

 

Thats where the Electronic Load Detector comes in at... It will speed the idle up, anytime a load is added to the engine.

Honda use a Speed/Density system to control the timing and fuel...

Hope that helps some...

 

For the idle to increase surely the more air must enter the engine, how can it do this.

 

Thats where the Electronic Load Detector (ELD) tells the ECU to speed up the EACV/IAC to let more air bypass it. So the idle will increase, to componsate for the added load put on the engine...

 

Here's how I understand it...

Honda's ECU reads the MAP sensor primarily to tell how much vacuum there is in the intake manifold. The TPS is taken into account to see what position the throttle's at. The throttle butterfly stays fully closed, or very nearly so at idle, so not much air leaks beyond the throttle plate. The idle primarily comes from the IACV on the back of the intake manifold - the I.dle A.ir C.ontrol V.alve. This is a small device, an electromagnet connected to a plunger. The computer sends a semi-sine wave signal to the electromagnet, causing it to snap on and off, thus opening and closing an orifice in the intake manifold, ie effectively creating a variably-sized vacuum leak into the intake manifold. This is also why you can listen to the IACV, to tell if it's working, by putting a screwdriver to it at idle and seeing if it's clicking. The idle adjustment screw is located at the intake side of this vacuum leak, and by adjusting the idle screw to allow more air to leak past it towards the IACV, the idle can be raised. However, the ECU can compensate the idle slightly upwards or downwards by varying the number of pulses it sends to the IACV. That means in order for the ECU to raise the idle it just speeds up its pulses to the IACV per time unit, and in order to lower the idle it can send less pulses to the IACV per time unit. So when the ECU detects load in one way or another, it can raise the idle, or when it sees the engine idling a bit too high after shutting off the electrical load, it can lower the idle.

From my experience the ECU is kind of retarded in the way it tunes the idle. It goes off a basemap which is defaulted to every time the car starts. This is why a car will run better after driving for 20 mins when it's in a bad state of tune (like my car =P ). The closer you are to the optimum idle, timing and fuel settings, the better the car will run.

Anyway I hope that made sense.

 

Yes you made prefect sense, Thanks for the help.