MAF & ISV

[s2avant]

I've just cleaned my MAF and ISV (Idle stabilisation valve). While doing this I've come across a couple of problems:

On the MAF the turbo side screen was stretched and starting to tear away from the metal rim. As a precaution I've removed it to stop bits of screen taking a rollercoaster ride through the turbo.

As for the ISV. It was sticking open so I gave it a good blast with carb cleaner. This got it all shiny and clean but revealed a somewhat more concerning issue. The section of the valve which rotates to regulate air flow has a big lump on the edge of it. It looks as though someone has had a go at it with a screwdriver. This makes the valve stick in the closed position.

I took it out for a blast and it picks up much better now and feels a lot stronger on boost. The real issue is my idle speed is now around 700rpm (it bounces from 500-700rpm before settling on 700). Before it was around the 900-1000rpm mark. I assume that 700rpm is too low.

Is this going to be caused by the ISV or would an air leak cause it? I know the ISV controls the idle speed but is this only when there is a load on the electrics (headlights, AC, etc) or does it regulate idle speed at all times?

I can live with it for now (even I can't get an ISV on a bank holiday monday) but will there be any detrimental effects?

Ben

[Beetie]

The ISV regulates idle speed at all times AFAIK, i would have thought now that everything is clean, i would check and adjust idle speed. Main cause for cleaning ISV is cutting out. Ben, does it cut out when approaching traffic lights etc after dipping clutch? If not i wouldnt really worry about it.
My screen on thr MAF is missing, due to the fact it was hanging off, and thought the same as you, so pulled the thing off completely (ooh err! ) At least it saves me getting the turbo repaired again!

[Stick Insect]

Ben, I feel that since you've cleaned the ISV the valve can close more easily and that is what is causing the lower tick-over.

My 2p worth.

David

[s2avant]

I'm going to order a new one this week. It's £190 + VAT!! Just for peace of mind. I'm driving down to Wales tomorrow to complete that section of 'coastal tour' so fingers crossed it doesn't embarass me while I'm there.

I got in it to go out for a spin last night and it wouldn't start. A few deft touches with the trusty 'tw@ing' hammer on the ISV and click all was well. The rpms are around 1200-1500 on warm up and then drop down to 6-700 when it's hot.

Ben

[Stick Insect]

I had the wrong ISV on my car and fitted the correct one. I will be getting the car tuned soon to set it up ok.
Yours may need a tune to work with the pepped up ISV.

it may be worth cleaning the isv once more as it may have gummed up again

David

[horvathg]

Ben, I feel that since you've cleaned the ISV the valve can close more easily and that is what is causing the lower tick-over.

My 2p worth.

David

I was also planning to do the ISV cleaning but backed when I noticed how tightly it was anchored to the block with ducts and cables..... Need another try.

[Stick Insect]

I was also planning to do the ISV cleaning but backed when I noticed how tightly it was anchored to the block with ducts and cables..... Need another try.

Gabor it's readily accessible on my car but the S2 is probably a different matter. Take a photo before and take your time. Cleaning the pipes out will be a good idea as well.

Mind you isn't that what you do for a job?

David

[horvathg]

Gabor it's readily accessible on my car but the S2 is probably a different matter. Take a photo before and take your time. Cleaning the pipes out will be a good idea as well.

Mind you isn't that what you do for a job?

David

I feel like going down and clean the ISV this time. I hope I can put it together afterwards. If not, you won't hear from me again.....

[dan_b]

When I took my MAF out for cleaning my turbo-side screen had the appearance of it having melted - it was torn and twisted and generally not a pretty sight. I took it out, can't really see what it's for anyway.

[horvathg]

When I took my MAF out for cleaning my turbo-side screen had the appearance of it having melted - it was torn and twisted and generally not a pretty sight. I took it out, can't really see what it's for anyway.

For those of you who wish to do an effective cleaning of the MAF thin wire I recommend the video casette recorder head cleaning spray, such as the one by CRC (Belgium). It is pure isopropil alkohol in a low pressure spray bottle with a long thin tube. It saves you the half liter bottled IPA you would need to soak the unit. Since the content comes out in a mild ray, it doesn't hurt the wire. I did it today, and the result was a shiny wire just in three minutes. The spray was intended for video rec head cleaning because it leaves no trace when dried up. Available anywhere.

[Alistair C]

Does anyone know how to test an ISV??

I know they are stepper motors inside so I guess you can't just put +12v across the terminals and expect the valve to close ??? Are they spring loaded to make them open again ??

cheers