Further to the poor idle / cold stumbling

[liuleichan]

I've been posting about my problem with my 98 S70 (2.5 10v auto) having intermittent issues with idling when cold.

So far, I've cleaned out the flame trap housing (numerous times), thoroughly cleaned the throttle body, changed the air filter, tried different plugs, checked the induction hoses for splits / leaks, and cleaned out the IAVC twice.

I've had the fault codes pulled, whilst it was having an oil change. The only code that the garage mentioned was an intermittent vehicle speed sensor fault? Looking in my Haynes manual, it states that the car doesn't have a dedicated one, and merely uses the ABS sensors.

I haven't discounted the IAVC from being at fault - to be honest, when the car is struggling, it does look to be idling to low. It could perhaps be another sensor. The car normally struggles on starting on the days when the problem occurs.

I mentioned to the garage all the things I'd checked so far - they're initial thoughts were that it would be some sensor. They suggested that an induction leak would be problematic all the time, rather than intermittently.

Any thoughts?

[Chris_Rogers]

I would suggest that the crankshaft position sensor and the camshaft position sensor signals are monitored for condition using an oscilloscope.

Also check the condition of the wiring to these sensors.

Other than that, try subsituting known good sensors.

[liuleichan]

>I would suggest that the crankshaft position sensor and the
>camshaft position sensor signals are monitored for condition
>using an oscilloscope.
>
>Also check the condition of the wiring to these sensors.
>
>Other than that, try subsituting known good sensors.

I have thought about the cam position sensor - especially given the occasional hard starting.

However, having looked at all the codes available, if an individual sensor were failing - and given there seems plenty of different codes for each sensor - wouldn't I likely have codes specific to any failing (even if intermittent) sensors?

I can't help but think maybe it is the IACV. When you look inside, there's a metal valve that moves slightly when you tip the motor.

Should that move quite freely and more than just a slight bit? Should the area that it covers, be opened and closed by simply tipping the motor? Or would that only happen under electronic direction?

[sholtby]

The IACV does have a part inside that is free to move ie if you shake the whole valve it swings from side to side within the valve.

Simon

[liuleichan]

>The IACV does have a part inside that is free to move ie if
>you shake the whole valve it swings from side to side within
>the valve.

How much movement should there be?

If you have the valve / motor off the car, and look down the pipe with the moving part, when you move it, should it completely open up that pipe?

Because on mine, it does move, but only moves a little bit, and not enough to properly open the gap, it merely moves a few mm.

[sholtby]

Its been too long since I had mine off to be sure. But I think it was more than a couple of mm. I just remember at the time that it seemed strange how loose the valve was and when I shook the whole valve you could hear it rattle.
Try drowning it with WD40 and push the valve gently with a screwdriver to see if it is still seized. Or wait and see if someone else can give you a better reply on how much movement there is.

Simon

[liuleichan]

>Its been too long since I had mine off to be sure. But I
>think it was more than a couple of mm. I just remember at the
>time that it seemed strange how loose the valve was and when I
>shook the whole valve you could hear it rattle.

I noticed that bit when handling it - you could feel it move.

>Try drowning it with WD40 and push the valve gently with a
>screwdriver to see if it is still seized.

I used carb cleaner, and WD40, and did try pushing it with a screwdriver, but didn't want to force anything.

Through the other pipe, there was a bit of gunk on what looks to be a circular bearing surface? That didn't seem to get properly clean, despite much spraying.

>Or wait and see if
>someone else can give you a better reply on how much movement
>there is.

Anybody else remember?

Hi there,

I have had poor idling before. I tried all the things mentioned already to no avail. Having said that, it was great to be able to clear out the throttle body...the amount of gunk was incredible. I digress!

If I were you I would try and change out the Mass Air Flow sensor for a known good one. I changed mine out last weekend and the difference was unbelieveable. I got the MAF sensor out of a 176k car for my own car (138k) and it has been wonderful.

Check to ensure that the flame trap piping is back together properly. This has caused issues for me as well in the past.

Another thing, after looking at your throttle body, did you replace the gasket with a new one? There could be air leaking there!

I have also heard (going to try and confirm this weekend) that the injector seals can cause issues. I have pulled mine out several times without any issues but I think I'll order some new ones up and put them in this weekend nonetheless.

Best of luck,

Colm

[Chris_Rogers]

The 10v does not have a MAF.

The idle air valve should be quite free and should move to completely open and close the shutter when the outside case is moved.
If yours does not then I would think this is the cause of your problem.

[liuleichan]

>The 10v does not have a MAF.

Quite - it has a MAP.

>The idle air valve should be quite free and should move to
>completely open and close the shutter when the outside case is
>moved.

By that do you mean that when looking through the pipe where you can see it, you should be able to make it fully open and close?

>If yours does not then I would think this is the cause of your
>problem.

Many thanks, that gives my much to go on.

If I can't make it work, I'll buy another one.