Idle speed valve query (1988 WBX 2.1 DJ)

[Mr Bean]

In the ten plus years I have owned my van I have never been able to detect the vibration claimed to indicate correct function of the Idle speed valve. However apart from a need to adjust the single throttle closed micro switch a few years ago I have had no slow running problems whatsoever and it does seem to function correctly and measures about five Ohms at the two pin plocket. The Haynes manual does show an image of the item on my engine section 4 B Fig 7) but the Bentley manual seems to be a bit skimpy on this particular area? Does anyone have the inside story on the workings of this gadget and the electrical signal which controls it.

[bigherb]

It is just a motor that turns against a spring, supplied by a square wave 12V pulsed signal (hence the humming) the longer the duration of the on voltage to off voltage turns the motor more opening the air valve.

[Mr Bean]

Yes makes sense as there is a similar device illustrated in the air cooled section of the Bentley's operating on the heated bi metal strip principle but none shown for the WBX. The use of PWM on a spring returned motor or solenoid operated valve would fit the function of the Idle speed valve on my engine. I had envisaged a solenoid in my Idle speed valve and would like to see inside although it doesn't come apart even if I were brave (stupid) enough.
Lack of vibration or humming is concerning but I guess if it is working OK I should leave well(?) alone.

[bigherb]

If you interested then this is from the VW training books, there are actually two types, the disc and a plunger type but both work on the same principle.

[Mr Bean]

If you interested then this is from the VW training books, there are actually two types, the disc and a plunger type but both work on the same principle.

Thanks yet again for that. My engineers predictive Xray vision had envisaged a solenoid and a linear slide valve but it clearly operates on a rotary principle and this is supported in the text. I am puzzled as to why, when I apply a gentle suction by mouth to the intake manifold port (No smart ass comments please ), that I detect a kind of pop or click and the valve seems to change state from close to open or vice versa. The reference to the failed safe mode in the text is both reassuring and concerning from my point of view as it could indicate a fault condition which accounts for a slight deterioration in tick smoothness over when my (albeit not yet run in exchange engine) warms up. It could be failed but in a kind of limp home mode. I have a PWM 12V variable DC power supply and may consider performing a test on the valve out of the vehicle of course. The plot thickens...

E D I T: For clarity - the unit on my engine has the feed from the air intake duct concentric with the shaft axis and not offset as in the unit illustrated.