Erratic IAC dual-solenoid output

[SamSpade]

I was bench testing my 3-wire Bosch (0 280 140 509) idle control valve:

and wired it correctly using INJFET ch6/ch7:

Figure from Rob's excellent user guide

The IAC valve behaves erratically, staying mostly half-open but continuously fluctuates.  Upon checking with the scope I see that some pulses from INJFET ch6 shorten unpredictably when the 2 waveforms should be exact mirror images of one another:

A = INJFET ch6 (EC36-6), B = INJFET ch7 (EC36-17)

Those erratic pulses from the first channel causes the IAC to behave erratically.

Here's the current IAC settings:

iac_speed = 6 --> PWM frequency = 1 / (4 + 6) ms = ~100 Hz
iac_max_steps = 128 --> sets half-opening of IAC at midpoint

Some other observations:

• I disconnected the Bosch ICV and instead connected the outputs to 10Kohm pull-up resistors to 12V.  The waveforms were still behaving erratically -- so it's not the ICV that has the problem.
• I changed the IAC dual-solenoid output settings to the P259 ch6/ch7 (EC36-31/EC36-32) without attaching the ICV (that would blow the P259) but connecting them also to 10Kohm pull-up resistors.  Exactly the same erratic behavior happens.  This means it's not the INJ FETs that have the problem.
• This happens on both firmware versions 1.0.73 and 1.0.78. I haven't tested with 1.1.x.

So it seems that it's a firmware issue, probably an event queue bug.  Anyone else experiencing this?  Does anyone know a solution?

[SamSpade]

Saw this other thread which is actually the same issue: General Discussion > Idle PWM - rattling sound?

I've just been given the following instructions: To stop the IACV clicking:
Set iac_cold_start_pos & iac_warm_start_pos to 0.

Setting both:

  iac_cold_start_pos=0
  iac_warm_start_pos=0

basically forces the IACV to fully close (or fully open depending on wiring) when the ignition is ON (engine not running).  It shuts off PWMing and turns the first channel totally OFF and the next channel totally ON.

Yeah, it's works to silence the thing.  Not sure though if the problem comes back with the engine running.  Maybe engine noise masks it.  Can't really say since I'm only bench testing. 

[gunni]

You´ll need to feed your VEMS a crank signal or a signal from the signal generator program.

This will allow you to bench test at various rpm´s and you can then check the ICV more thouroughly.

I´ll be doing bench testing soon to try and create settings for the BMW 3pin ICV so that it behaves quietly
Mine at the moment makes a hissing sound as it closes and opens.

[GintsK]

Solution is simple: put IAC actuator speed to 0.
No need then adjust strating position to 0.