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Query re throughput of "Closed" Bosch Idle Valve


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Morning "wiser ones than I",

I'm foraging forth in my aim to be "the longest time to complete a Megasquirt installation"...

I'm currently on another push to finish my 110 and as it is a 4.6 plenum, needed to install an idle valve.

One of my errors, (which I realised recently) was that I had removed the stock idle valve, blanked off the entire ID with a snug length of hose, then capped it with a little alloy plate. This accidentally blanked off the hex idle screw....

I've now got it idling at about 1000rpm with the hex screw and adjusted the stop under the throttle lever. It does not like going lower than that at the moment.

I've got a 2 wire Bosch idle valve (from Nige) which i believe is out of a Volvo?


I tested it with 12V and indeed, the little rotor rotates to expose more area but when there is no power to it, there is still quite bit of throughput.... When you look down the outlet, you can see the shutter is not the full width of the outlet. Is this normal?


If so, I presume it is normal then to have to reset the plenum screws to lower the idle again once this valve introduces its air contribution to the inlet, even when "off".

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It is normal to be open when unpowered, so if it fails, the engine doesn't stall.

At a certain duty cycle it will be closed :) you need to test and find this out.... Wire it up, set a duty cycle for pre-start, and look at the valve position to see if closed or not, repeat until closed.

I'm becoming more convinced these idle valves are not really required though.....

The other way to drop idle speed is to lower timing advance.... This helps give a nice stable idle, drop timing, open air screw, drop a but more.... If you just drop the idle cells, you get very good self-recovery from a stumble, and as load increases, it moves cell to where there is more timing, again picking up more idle speed :)

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Thanks Bowie...

Time for a little update - By peering at it, I was convinced that the "gate" in the idle valve was not full width (see photo above) but hooked it up to the loom a couple of nights to try anyway.

I messed around with the frequency settings as suggested with no luck, then did some googling to see if anyone else had figured it out.

TomG (on here) had done some trials in May 2007 but he had a Bosch IAC valve (0280 140 505) and needed to install a diode to bring it alive. My shoulders dropped a bit when I saw that, although I have a Bosch 0280 140 516 but I thought I'd try the settings he used anyway (without the diode).

Valve Frequency 200

Crank 90

Minimum 70

Closed 60.

Amazingly, looked in the valve and it was totally shut. I figured that that was probably because I'd had the engine running so it was warm enough, so would have to wait for it to be cold to see if it opened...

Last night, rather than pull the hose off to see if it was open while cold, I flicked the key and she burst into life, then happily sat idling at 1000rpm.

Bingo. MOT is now booked (again) to see if I can get a "pass" that will let me take it out for tuning runs...

Thanks again!

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