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PWM idle in Open loop

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Hi all

Car is running quite well now (much better than it was with the weber) although in closed loop it does hunt a bit sometimes. So, I tend to run in Open loop (Warm up only) but I can't find a way of closing the PWM, so only get a fast idle at around 1,100 rpm. I have set the closed(dc) to 25 which should close it, but this is greyed out in open loop mode so it goes back to default and stays open. Data logging shows the idleDC at 0% at idle.

Am I missing something here, or do I have to run in closed loop to get an idle at 800rpm?


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How do you know a DC of 25 will close it? Have you tested it? Every valve varies.... So only way is really to test, and then use that as your closed value.

It is perfectly possible to set the idle at 800rpm in open loop.

What have you set your base idle to? (Pwm pipes blocked, set with quarter inch hex key next to throttle body on plenum)

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I googled the part number and somehow found this thread -

I must admit that I have it running without altering the idle screw as I didn't realise there was an adjuster under the plug by the throttle body. There is no mention of this anywhere in the tuning manuals, although adjusting the throttle stop is mentioned a few times but I don't appear have one of those. I only found this air bleed while googling something or other about a week ago.

Testing was going to happen today, but other things got in the way, so it will be tomorrow. Before doing this, I wanted to get some information about the PWM as I have read that the PWM valve is closed when 3.5V is applied to it. It is open when no voltage is applied and goes to default of fast idle. As open loop applies no voltage to it, it remains at fast idle. Hence my question, which was to clarify what to do about it.

I have read that a base idle of 600rpm is good to start, is this about right?

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One of the settings for open loop is the DC for normal, hot idle, this is what you need to set, then you end up with the correct voltage (actually current...) applied to close it. I don't remember the term, as my head is in MS2.

I'm afraid I can't confirm the numbers for you, and would only recommend using them as a ballpark figure. Testing is the way to go, as I think you know :)

600 is a good base ideal, yep.

If you are getting hunting at idle, I would also check your spark and fuel maps around this point, and experiment, with the closed loop pwm disabled. I have managed to get nice stable idle without having to resort to closed loop at all...

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