Hello all, I have been trying to track down my idle issue for a while now and I have had limited success. I was hoping to get some assistance from people who know much more than I do. My car is a 1987 325e.
First off, when the car is started, it surges to 2-3k RPMs. Then, it will settle at about 900-1100 rpm. It idles slightly higher when warm. The idle will usually vary up and down by about 100 rpms, and it is more stable when cold. Turning on the air conditioner makes it more unstable. Usually, when letting off the throttle when the engine is warm, the idle sinks to 1000 and then jumps up to about 1500 before settling back down.
Now, let me talk about my troubleshooting so far. First, I checked for operation of the ICV when the ignition is turned on. It does not buzz when the ignition is on, and the valve does not move. This should mean that the idle control system is not working due to a bad idle control module or bad valve. I then try starting the car with the electrical connector disconnected from the valve. Given that it seems to not be working at all, this should not have an effect on idle behavior. However, when the car is started like this, it starts up and surges to 2000 and then keeps going. The rpms keep rising, and then I shut the engine off so it will not keep going. After about 10 seconds, it had reached nearly 4000 rpms. This is very strange behavior and I really don't understand how removing the valve's electrical connection would cause this.
I then looked at the inputs to the ICM. As per the tests in the Bentley manual, the inputs all seemed normal. The ICM is a rebuilt unit from ProgRama. The throttle position switch was working correctly.
It seems like at this point the fault could either be with a bad control module or a bad valve. What I don't understand is how disconnecting the ICV could cause the engine to surge uncontrollably. The default position of the valve is fully open, and when the electrical connection is applied, the only effect it has is closing the valve to adjust the idle speed. The system is non-functioning, but somehow disconnecting it is causing even stranger behavior. I have read a lot on the way the idle system works in eta cars, but I'm still stumped. Any suggestions would be very appreciated!
First off, when the car is started, it surges to 2-3k RPMs. Then, it will settle at about 900-1100 rpm. It idles slightly higher when warm. The idle will usually vary up and down by about 100 rpms, and it is more stable when cold. Turning on the air conditioner makes it more unstable. Usually, when letting off the throttle when the engine is warm, the idle sinks to 1000 and then jumps up to about 1500 before settling back down.
Now, let me talk about my troubleshooting so far. First, I checked for operation of the ICV when the ignition is turned on. It does not buzz when the ignition is on, and the valve does not move. This should mean that the idle control system is not working due to a bad idle control module or bad valve. I then try starting the car with the electrical connector disconnected from the valve. Given that it seems to not be working at all, this should not have an effect on idle behavior. However, when the car is started like this, it starts up and surges to 2000 and then keeps going. The rpms keep rising, and then I shut the engine off so it will not keep going. After about 10 seconds, it had reached nearly 4000 rpms. This is very strange behavior and I really don't understand how removing the valve's electrical connection would cause this.
I then looked at the inputs to the ICM. As per the tests in the Bentley manual, the inputs all seemed normal. The ICM is a rebuilt unit from ProgRama. The throttle position switch was working correctly.
It seems like at this point the fault could either be with a bad control module or a bad valve. What I don't understand is how disconnecting the ICV could cause the engine to surge uncontrollably. The default position of the valve is fully open, and when the electrical connection is applied, the only effect it has is closing the valve to adjust the idle speed. The system is non-functioning, but somehow disconnecting it is causing even stranger behavior. I have read a lot on the way the idle system works in eta cars, but I'm still stumped. Any suggestions would be very appreciated!
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