Quote:
Originally Posted by Rversteeg
Never in my over 500K km of driving my 940LPT have I had to adjust the idle setting, so I cannot tell you how it is done by heart. All I ever did was cleaning the throttle house body.
The basic idle speed of 500 rpm is set by letting just enough air past the throttle plate. Additional air to reach 900 rpm is byapssing the throttle, through the IAC valve. The IAC is the only means of the engine ECU to control the idle speed. In other words, minimum idle speed is always 500 rpm, the speed above this is controlled by letting more or less air bypassing via the IAC valve.
The ECU uses information from the TPS to ascertain it has to adjust the engine speed and that a higher than idle engine speed is not caused by you pushing the throttle pedal. A speed signal is used simultaneously to determine if a higher than idle engine speed is not caused by the vehicle braking on the engine. It is an on/off switch and does nothing to the idle speed itself. That is entirely done by the ECU and cannot be adjusted externally.
You can only adjust the minimum idle speed via the throttle plate leakage ratio. If you set this for example to 1200 rpm, the ECU will have no means of controlling the engine speed any lower than 1200 rpm. With the correct setting of 500 rpm, the ECU has enough bandwidth to control the idle speed via the IAC valve. Minimum idle speed at 500 rpm with IAC valve closed and maximum idle speed of about 1500 rpm (?) with IAC valve maximum open.
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Got it. Thanks for the explanation. When you don't know a certain thing, sometimes a bit of info, that is massively useful to someone who does understand it fully, can send you on a goose chase or just scratching your head.
I don't fully understand this system. I don't get what is the pupose of the adjustment screw or why it needs to be between 0.15 to 0.45 if the throttle lever is fully close anyways when the car is idling at the proper rpm. Not asking for an explanation. Just saying.
What matters is that the car is idling better than it ever was. It does bother me a lot not understanding things and how they work. But not being a naturally mechanically inclined personal, i have to start accepting that sweedish engineers just work in mysterious ways.
Thanks to the good folk in this forum i've learned so much. I couldn't change a spark plug before.
