05-10-2020, 02:57 PM
I've seen a few idle speed instability complaint on the CB1100', there's too many pages to read, so I only read a few treads.
Let me explain the proper operation of the Idle Air Control Valve (IACV).
Construction of IACV:
The IACV valve consists of 4 coils and a rotating plate.
The plate covers/uncovers an air bypass passage to control the required speed.
Each coil resistance is roughly between 90 ~ 120 ohms.
ECM idle speed control:
From the ECM internal schematic on the IACV diagram, the ECM controls the idle speed via the 4 coils inside the IACV.
The ECM grounds the coils in sequence to control the air bypass opening.(1A pin A6, 1B pin A7, 2A pin A17, 2B pin A16)
Example:
To increase the air bypass therefore more speed; the ECM grounds in sequence 1A, 1B, 2A, 2B (repeat if necessary) so that the plate rotates CW and uncovers the bypass port.
To decrease the air bypass therefore lower speed; the ECM grounds in reverse sequence 2B, 2A, 1B, 1A (repeat if necessary) so that the plate rotates CCW and covers the bypass port.
As an example, (I am assuming) from "fully" closed position to "maximum" open position there are 80 steps
If you have a HONDA scanner you can monitor the number of steps at idle.
Now let's say the engineer decided that with a fully warm up engine when the ambient temperature is at 71 F, the steps (count) should be around 30 steps for 1000 RPM (Now this 30 steps is now known as the idle "target" speed and the ECM will try to bring the IACV opening to 30 steps so that the engine speed is 1000 RPM.
But in real life situation if there is an air leak after the throttle body and in order for the ECM to maintain that same 1000 RPM, the ECM now has to decrease the IACV steps (closing the bypass port) to let's say 20 steps to compensate for air leak.
Now, if the is an intake restriction, the ECM will increase the IACV steps to let's say 40 steps to let more bypass air in (opening the port).
If you have a scanner, you can immediately deduct that the IACV is closing or opening the bypass port to compensate. So having no scanner one is a just guessing game.
What important input sensors are required for the ECM to decide the idle speed.
1. The Throttle position Sensor will tell the ECM to control speed for idle. (most important signal for idle speed)
2. The MAP sensor will tell the ECM how much air is entering the engine.
3. The Engine Oil Temperature (EOT) will tell the ECM to compensate for a cold morning start so that you can get a fast idle.
4. The Intake Air Temperature (IAT) will tell the ECM to compensate for air density.
IACV does not easily fail
If coil resistance are on specification, then the IACV may be sticking due to dirt or rust etc. It can easily be cleaned with brake cleaner or equivalent.
Note: Each time when the engine is shut down, the ECM will open the IACV valve to maximum and ready for the next start and then go into sleep mode - and also
because the ECM needs to know its position (which step it is in usually at 80 steps).
Hope this will help understand the operation of the IACV.
Let me explain the proper operation of the Idle Air Control Valve (IACV).
Construction of IACV:
The IACV valve consists of 4 coils and a rotating plate.
The plate covers/uncovers an air bypass passage to control the required speed.
Each coil resistance is roughly between 90 ~ 120 ohms.
ECM idle speed control:
From the ECM internal schematic on the IACV diagram, the ECM controls the idle speed via the 4 coils inside the IACV.
The ECM grounds the coils in sequence to control the air bypass opening.(1A pin A6, 1B pin A7, 2A pin A17, 2B pin A16)
Example:
To increase the air bypass therefore more speed; the ECM grounds in sequence 1A, 1B, 2A, 2B (repeat if necessary) so that the plate rotates CW and uncovers the bypass port.
To decrease the air bypass therefore lower speed; the ECM grounds in reverse sequence 2B, 2A, 1B, 1A (repeat if necessary) so that the plate rotates CCW and covers the bypass port.
As an example, (I am assuming) from "fully" closed position to "maximum" open position there are 80 steps
If you have a HONDA scanner you can monitor the number of steps at idle.
Now let's say the engineer decided that with a fully warm up engine when the ambient temperature is at 71 F, the steps (count) should be around 30 steps for 1000 RPM (Now this 30 steps is now known as the idle "target" speed and the ECM will try to bring the IACV opening to 30 steps so that the engine speed is 1000 RPM.
But in real life situation if there is an air leak after the throttle body and in order for the ECM to maintain that same 1000 RPM, the ECM now has to decrease the IACV steps (closing the bypass port) to let's say 20 steps to compensate for air leak.
Now, if the is an intake restriction, the ECM will increase the IACV steps to let's say 40 steps to let more bypass air in (opening the port).
If you have a scanner, you can immediately deduct that the IACV is closing or opening the bypass port to compensate. So having no scanner one is a just guessing game.
What important input sensors are required for the ECM to decide the idle speed.
1. The Throttle position Sensor will tell the ECM to control speed for idle. (most important signal for idle speed)
2. The MAP sensor will tell the ECM how much air is entering the engine.
3. The Engine Oil Temperature (EOT) will tell the ECM to compensate for a cold morning start so that you can get a fast idle.
4. The Intake Air Temperature (IAT) will tell the ECM to compensate for air density.
IACV does not easily fail
If coil resistance are on specification, then the IACV may be sticking due to dirt or rust etc. It can easily be cleaned with brake cleaner or equivalent.
Note: Each time when the engine is shut down, the ECM will open the IACV valve to maximum and ready for the next start and then go into sleep mode - and also
because the ECM needs to know its position (which step it is in usually at 80 steps).
Hope this will help understand the operation of the IACV.