gcfcos

Hey guys little help needed. My saph cos 4x4 has a poor idle, when cold on "choke" it idles fine but soon as it starts warming up the idle will drop down suddenly and rev itself up to keep itself running and then idle for 5 seconds ok on its own and then the idle will drop down almost to the engine cutting out and it revs itself up in order to keep itself running. It has a stage 3 msd chip but with my old stage 1 pts chip it will run and idle fine?? I was told by msd to disconnect the idle control valve and set the base idle and then to plug it back in and it will re set itself but it's still doing the same thing. Anyone else experienced this? I've Taken the iscv out and stripped it and cleaned it

Loomer

There are many causes of issues like this which are mainly covered in a set up like air leaks, fuel pressure, sensor alignment, co trim, ecu voltages, throttle pot calibration, so many things can make a big difference, but if your 100% sure the car is set up well,maybe it needs a little touch of fuel adding into the map to stabilise it ? What is the AFR/CO level? Is it closed loop controlled? If so maybe the closed loop correction strategy needs a little bit of work to suit your engine.

gcfcos

Hi thanks for the reply. It doesn't have closed loop, it's just a basic stage 3, greens and 3 bar etc with a stage 3 msd chip. It idles fine with the stage 1 pts chip. My friends Cossie has the exact same set up which I fitted for him and his idles fine. Could anyone tell me how to test the iscv? And what voltage etc I should be getting just to rule it out. Thanks

Loomer

If the base idle is set correctly with the Iscv unplugged then it should never drop below this. The valve only opens and closes, when it's closed it should sit on the base idle which you set at 900 rpm.

If the idle still is unstable it can sometimes just be that the map is referencing a load site that's not quite suited and it has a big effect in the idle speed and it will be bobbing about picking up on these sites.

You can do some testing your self, ie what is the Co level? Can you richen it up and does that help? Does adding .1 .2 .3 .4 .5 bar of fuel pressure fix the idle stumble? If so you can relay this info back to msd and they can try to fix it in the chip although it's often hard to know where it's referencing and what load site it's on which is why bits like this are so easy to fix when mapping live, but can be a nightmare to try and fix off the shelf

gcfcos

I've set the co up on the gas analyser at work to what msd told me to, (from memory I think it was 2.5%) but it was a while ago and I could be wrong. It was very hard to set the co up accurately with it hunting but I'm thinking of taking the car back Into work and setting the idle up with the iscv unplugged so the idle is stable and then set the co up while its idling stably and then plug the iscv back in and see what happens? Failing that I'll save up and get it booked into a rolling road but wanna try and fix it myself first. Thanks again for help

Loomer

If it idles ok and stable with the valve unplugged, that would indicate the mapping is suitable, 2.5% co is fine and pretty much all ybs will idle steady there.
If so check the tps cal, and then strip the valve and inspect the spring tension under the piston. Make sure it's rebuilt properly. I see loads of valves badly built up causing idle problems and making the valve constantly pass air.
It could still mean the load sites around idle that you reference as the manifold depression changes when the Iscv operates need a bit of work.

gcfcos

I've had the valve out and stripped it, cleaned, oiled and rebuilt but made no difference :-( yes with or unplugged I managed to set the idle to 900rpm and it sat there idling happy. Perhaps it's worth trying another iscv in there. Would it do any harm to leave the iscv disconnected long term? Thanks again for all your help

Loomer

There's really no need to run with them unplugged if things are right. It will be a pain cold without it.

Tps cal has a big effect on the Iscv operation. So that's worth checking, also Spring tension on the inner spring in the valve

gcfcos

I think I'll do the setting up at work with it unplugged and see what that does, if not I'll fit a new one and see what happens

Loomer

Most new ones I've seen are very poor with the wrong Spring rating. I'd avoid the shiney Chinese ones like the plague and you won't find much else new these days.
They just dont work properly.
When needs must I strip them and fit the old springs from the oe valve in them which makes them ok to use, but the fact is if the old one is changing idle speed the valve itself works, it just needs to be built up properly

gcfcos

Yeah I defo wouldn't fit Chinese parts to the Cossie. I'm taking it into work tomorrow to have a play while its hooked up to the gas analyser

gcfcos

Well took it to work today and after setting up the co and idle with the iscv unplugged and then plugged it back in afterwards it's mint happy days, so nice to have a steady idle !