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Idle Valve Stuff

I use a BOSCH 2 terminal spring loaded type no. 0 280 140 531 from a 91' porsche car. Its a straight type with inlet and outlet 180° apart. It's the original part used on the 911 porsche in 1989 to 1992, and fit's the intake system i got for my car.

It measures 8.7ohm DC resistance thats quite a heavy load.

I use iac_sol_channel=60 for IAC output, thats the injector G output.

I experimented with mdi00..mdiff command to se the valve open and close, and it seems to work. But i gets VERY Hot. Maybe in the original Motronic application it is not ON all the time. Could it be that it is only activated when the Idle Switch on the throttle housing is activated ? I dont have a working car to confirm that.

Old Q&A

The PWM Frequency is way to high for this old Motronic Idle Valve, it should maybe oprate at 100Hz not 2KHz.

I have been lookin in softpwm.c and iac.c but i do not understand what's going on in the code (I'm not used to C programming). OK i see that the PWM duty cycle is set in iac.c with this.

	softpwm_set(&idle_pwm_soft, pos);

but i dont see any frequency settings in the init_iac procedure theres just one statement.

        softpwm_init(&idle_pwm_soft, 0);

AFAIK there is no way to change the PWM frequency in config but it should be an easy hack. But instead of doing that it may be good to look at the the mechanics. The valves i have on my Audis consume between 2 and 4A depending on model and the plungers are very heavy to act as a proportional valve instead of a PWM valve. I think this is how most idle solenoids work. When thinking about the power over the valve you find 1.4AX14V=19,6W over yours and I find 4X14=56W over my nastiest idle valve. This is a lot of power and if used in the lab without airflow it will get hot, I suspect that it's cooled by the air flow through the valve when used in the car.

I can't see how the high frequency would make the valve run hotter then PWMing the current at a lower frequency. The FET and the flyback diodes may on the other hand get hotter at this frequency then at 100Hz. An easy test would be to check if the solenoid runs hotter at 80% then it does at 100%. I suspect that it doesn't.

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