I have a question about the one in my 924s. I have had a low vacuum problem in my car and on deceleration it would intermittently act like the throttle was hanging or some one was blipping the throttle a little. This weekend I cut the ISCM out of the system (this also cut out the evap system as well). I did this by disconnecting the tubs and vacuum lines from the intake and blocked all tubes. I plumbed the brake master directly in to the manifold. The car runs great now so obviously there was an issue there some where.
In chasing the problem I stripped off every piece of vacuum hose and the intake and re sealed everything and this did not solve the problem. While I was going this I tested the ISCM by applying voltage to it and the valve would open and close depending on the polarity however it did not snap back to either open or closed when the power was removed (I assume it should snap back to closed).
My question is this. It was my understanding that they are controlled by a pulsing power supply. By varying the pulse width / rate you varied the amount of air they let in to the intake, this pulsing was then countered by a spring on the valve that would close the valve when ever there was no power to it. Is this correct? If this is the correct operation of these things then can I assume that mine is malfunctioning as it is not returning to the closed position?
Some of the older units used on the CIS cars are based around ambient temperature and open of close when power is applied. These have two connections.
There is a middle version used in early Bosch-based EFI systems that are simple DC electric motors that open and close fully depending on which way power is applied. Very basic and simple, but binary in their use. These usually have two or three connections.
The later versions used in EFI systems are actually stepper motors that require a proper electronic circuit to open and close them properly. These usually have 4-wire connections. Much more finely controlled by the EFI system.
Sounds like you might have shaft seals that are leaking.
In the unit itself, since removing it improved your idle. So its leaking someplace.
I was wondering that or since it also resulted in me disconnecting the Evap system it may be related to that. In either case I need to sort it and unforchinitly winter is coming so I will probably forgo fixing it proper until spring. In the mean time I will put some sort of manual idle speed control on it so I can bump the idle speed on cold mornings.
wclark
Reader
10/16/13 3:36 p.m.
In reply to dean1484:
What is the Bosch part number on the ISV? There are a couple types and they are driven (electrically) in different ways (e.g. Single polarity PWM, dual polarity PWM).
The single polarity PWM type usually power fail to a slightly open position (it is actually the zero position on a motor with a return spring and stop, but the way the valve is cut it goes 100% open at a high PWM duty cycle to 0% open at a smaller PWM DC then past that to about 20% open at 0 PWM DC).
