[Rein_FOST]

Hi all

Trust all is well.

My cars idling suddenly changed. On cold start (cold engine) for when car stood for overnight or 8 hours moreor less during work day.

It will idle fine at 1200 rpms and as engine warms up and revs begin to drop to 800rpms it will ilde fine and then suddenly start to spike again to 1200 and drop back to 800.

This continues for another 30odd seconds till it idles normally at 800.

I did a visual inspection on the vacuum line that runs from plenum but couldn't see a fault.

What could be causing this other than perhaps a vacuum leak?

Car is the st225 2.5l.

Kind regards

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[elyk864]

Hi all

Trust all is well.

My cars idling suddenly changed. On cold start (cold engine) for when car stood for overnight or 8 hours moreor less during work day.

It will idle fine at 1200 rpms and as engine warms up and revs begin to drop to 800rpms it will ilde fine and then suddenly start to spike again to 1200 and drop back to 800.

This continues for another 30odd seconds till it idles normally at 800.

I did a visual inspection on the vacuum line that runs from plenum but couldn't see a fault.

What could be causing this other than perhaps a vacuum leak?

Car is the st225 2.5l.

Kind regards

Sent from my F8331 using Tapatalk

Iv'e been getting some odd idle issues also, but car has thrown a Evap Leak code a couple times now. I just need to take it in and get that fixed. I googled it a bit and it seems to be a common problem so it should be an easy fix.

 

[XRJoe]

Hi all

Trust all is well.

My cars idling suddenly changed. On cold start (cold engine) for when car stood for overnight or 8 hours moreor less during work day.

It will idle fine at 1200 rpms and as engine warms up and revs begin to drop to 800rpms it will ilde fine and then suddenly start to spike again to 1200 and drop back to 800.

This continues for another 30odd seconds till it idles normally at 800.

I did a visual inspection on the vacuum line that runs from plenum but couldn't see a fault.

What could be causing this other than perhaps a vacuum leak?

Car is the st225 2.5l.

Kind regards

Sent from my F8331 using Tapatalk

Could be a sensor issue as well. Has the weather changed recently where you are? Assuming somewhere in Europe.

Has the car been remapped? Any mods?

 

[Rein_FOST]

Hi @XRJoe

No, no weather changes. The does have an unknown map. I am planning on doing an stage 2 upgrade at the end of next month.

Ill remove and clean map and maf sensors on the weekend and see if there is an improvement.

If not I guess I then need to take it in. I have displaced my obd scanner so waiting on new one to check for any errors.

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[LMStone510]

It's normal, at least according to Alex at Stratified when I asked him.

There are as you know even in the stock tune a gazillion tables for timing, idle etc. etc. etc...

The car runs a faster idle driven by some tables to warm up the catalytic converter. There are other tables that control idle speed based on whether the car is warmed up or not.

Alex described to me that, as the car is warming up, these two (sets of?) tables conflict, and the idle will hunt some for a few minutes. Blip the throttle and it almost always goes away. But if not, no big deal as it will go away when the car warms up anyway.

BTW, a minor vacuum leak will not result in an idle speed increase, because our cars have MAP, not MAF sensors. The car just adjusts fuel to a desired mixture and doesn't care too much where the air is coming from (within reason).

Hope that helps,
Mark

 

[Rein_FOST]

Thanks @LMStone510.

That makes sense yes, I actually did read about that tables somewhere when I was looking at something else.

I was only worried because the car never did that. It would have just idled at 1200 at startup and drop to 800. This just started from last week so was a bit worried.

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[XRJoe]

It's normal, at least according to Alex at Stratified when I asked him.

There are as you know even in the stock tune a gazillion tables for timing, idle etc. etc. etc...

The car runs a faster idle driven by some tables to warm up the catalytic converter. There are other tables that control idle speed based on whether the car is warmed up or not.

Alex described to me that, as the car is warming up, these two (sets of?) tables conflict, and the idle will hunt some for a few minutes. Blip the throttle and it almost always goes away. But if not, no big deal as it will go away when the car warms up anyway.

BTW, a minor vacuum leak will not result in an idle speed increase, because our cars have MAP, not MAF sensors. The car just adjusts fuel to a desired mixture and doesn't care too much where the air is coming from (within reason).

Hope that helps,
Mark

Thanks @LMStone510.

That makes sense yes, I actually did read about that tables somewhere when I was looking at something else.

I was only worried because the car never did that. It would have just idled at 1200 at startup and drop to 800. This just started from last week so was a bit worried.

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Just remember we're talking about the Mk2 ST225 (2.5l Volvo motor). I'm not sure what from the Mk3 ports back over to the older engine and management.

 

[Rein_FOST]

Since idling is runnig of tables which is based on air density I guess.

Could it be that one of the lambda sensors is not working properly or on their way out. As the also measure air and I know some of them have an heating element to warm the sensor for when exhaust is still cold.

So if cold or not working properly it sends wrong values and then wrong readings is made from idling tables?

I don't have cel on. Will scan tomorrow to check if I have any dtc codes.

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[LMStone510]

Thanks @LMStone510.

That makes sense yes, I actually did read about that tables somewhere when I was looking at something else.

I was only worried because the car never did that. It would have just idled at 1200 at startup and drop to 800. This just started from last week so was a bit worried.

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Sorry; until XRJoe pointed it out I didn't realize you had a 225. I have no experience with tuning/mapping of that generation, so can't say for sure if what I offered earlier is correct for your car.

I can say however that my car didn't start hunting until at least two years after I had it as I recall.

All the best,
Mark

 

[Rein_FOST]

No problem, and thanks for the input.

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[Rein_FOST]

Some feedback.

I got my new diagnostics tool and scanned for dtc codes. Sure enough two came up: P0420 which is a generic code for lambda sensor failure or o2 related issues and then the actual issue I suspect : P2237 which is heater circuit open or shorted.

I then also read that it has a fuse/lug as well which should be 20amps. Upon checking there was a 15amp fuse in the position and didn't seem blown. I replaced it with a 20 amp fuse in any case.

Could the fuse be an issue as I haven't testes it yet as car needs to cool down. If not then need to change the sensor.

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[Rein_FOST]

Seems either the fuse or unplugging the sensor and connecting it resolved the issue. The plastic is broken from the sensors connection so it might have also wiggled a bit loose. So just taped it with some electrical tape.

Tested car this morning and late afternoon after it cooles down and idle seems to be normal again.

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[XRJoe]

Glad you seem to have found it!