Author Topic: ISV Operation  (Read 2171 times)

Offline dubstar

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ISV Operation
« on: March 12, 2012, 10:22:23 am »
My understanding is there is a bi-metal strip inside, so when it's strapped to the steel water pipe on the back of the block, with the pipe heated by the water the disc inside reveals a larger venturi.

So having been warned it's a sod to get to once it's built up and in the car, I thought I'd check it's operation beforehand. I've put it on a radiator I can hardly touch at work (as it's that hot) on a nice flat surface, and although there is movement, it's not moving a deal.

What am I looking for? At the minute going from cold, it's leaving say 5% open (although it's a strange shape) to fully open with heat? Mine ain't moving that much.

I understand that the heat will move the bi-metal strip and therefore the disc & send a signal to the ECU, but what function does linking it into the boost side of your induction have? Is this just to aid the warming up process? Is that why I can't get it to open fully?

Basically, I don't get it - and I'm sure it's very simple!

Offline Andy

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Re: ISV Operation
« Reply #1 on: March 12, 2012, 12:40:57 pm »
The two wires going to it are ignition and ground. All they do is power an internal heating element which heats up the bi-metallic strip inside the valve and closes off the air bypass as it warms up.

I presume they bolted it to the water pipe to give an intermediary opening stage, so a warm engine restart ends up with a slightly lower initial idle than if the motor was stone cold.

Stick 12V up its arse and see if it closes up.

Offline dubstar

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Re: ISV Operation
« Reply #2 on: March 12, 2012, 10:09:47 pm »
Cheers Andy.

When I load it up with 12v, it gets warm & shuts completely as you suggested.

When there is no voltage and it's cold, it only opens up this much though..... Not a lot. In fairness, there are no witness marks which I can see which would make me think it would open any further, but if you, or someone, had a working one which they could confirm is the same in the cold state, it would put my mind at rest - as I know these can be troublesome and I don't want to build in problems!




Offline Jezza-7

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Re: ISV Operation
« Reply #3 on: March 12, 2012, 10:55:52 pm »
Does the G40 ISV do a different job to the G60 one?

Idle Valve - The G60 uses an electronically controlled idle valve that bypasses the closed throttle to feed a controlled amount of air into the engine and sustain an idle. These often become sticky and work erratically (causing a hunting idle) or cease working at all. In most cases that can be fixed with a quick clean. Remove them from the car and soak in petrol or carb/injector cleaner before rinsing, drying and refitting. Check also the pipes to and from the valve for air leaks as these can also cause idle problems.

The idle valve also acts as a boost limiting system. When boost reaches a certain level the ECU sends a signal to the valve to open a solenoid that bleeds excess boost out of the system and into the boost-return pipework. Some people have fitted check valves to prevent this excess boost being bled off. These should probably be removed as not only does the ECU open the valve to bleed the excess boost off but it stops retarding the timing. If you retain this extra boost the timing will be too far advanced as the check valve makes no adjustment to the timing for the extra boost and thus the engine is likely to pink.

Offline Andy

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Re: ISV Operation
« Reply #4 on: March 13, 2012, 07:23:01 am »
G60s use an idle stabilisation valve which is actively controlled by the ECU to limit boost pressure and control idle speed as per your description. The G40 one is really just an auxiliary air valve that's a passive component.

Ross - I'll try and grab a pic of mine for you.

Offline Jezza-7

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Re: ISV Operation
« Reply #5 on: March 13, 2012, 07:57:35 am »
Ah i see, cheers for clearing that up Andy!

Offline Andy

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Re: ISV Operation
« Reply #6 on: March 13, 2012, 07:11:32 pm »

Offline dubstar

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Re: ISV Operation
« Reply #7 on: March 13, 2012, 09:01:21 pm »

Nice one Andy.

It looks a little more open than mine cold, but I'm not splitting hairs. It's going on. End of.

Thanks a lot!

Offline Andy

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Re: ISV Operation
« Reply #8 on: March 13, 2012, 09:25:13 pm »
She'll be reet!

Offline boyzey

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Re: ISV Operation
« Reply #9 on: March 14, 2012, 08:03:31 pm »
whilst wer on the subject, does any one no if the gt isv is the same as the g40 one, been told they have different part no but have neva had a gt one to compare

Offline Andy

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Re: ISV Operation
« Reply #10 on: March 14, 2012, 09:33:43 pm »
They are different part numbers, I think physically they're the same though - just that the tension in the bi-metallic strip is different.

Offline boyzey

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Re: ISV Operation
« Reply #11 on: March 16, 2012, 08:28:39 pm »
ye thought id being told they look same but different numbers, gt isv might do same job then or something like might have to compare side by side cheers

Offline bawbag

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Re: ISV Operation
« Reply #12 on: June 03, 2021, 03:42:37 pm »
Hi just checking in on this as I'm having some idle problems that I think are due the ISV not working and probably needing a clean. What's the best way to remove it? I have a GT not a G40 so i assume it will be a similar way, does it involve taking the inlet and everything else off? Or can you get it out from the back, it looks like 1 bolt holding it in, is that right is there another hiding?
Any advice appreciated thanks!
« Last Edit: June 03, 2021, 04:10:48 pm by bawbag »