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Old 01-03-2020, 06:33 AM   #1
Fa182
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Default Rolling idle when warm (940T)

New year, old issues to resolve

I've made a thread before about the idle on my 97 940T, but that wasn't exactly about this issue. I've been thinking more about it since.

When the engine is warm, I have an idle what I can basically describe as a sinus curve. It always rolls up and down and the car noticeably shudders when it's at the low point.
It only starts doing this after like 10 mins of driving.

The second issue is that (also only when the engine is warm), the car starts fine but the revs dip down quite a bit for a second or so. This happens after every start and only when the engine is warm.

Videos of both below.

Now, isn't that maybe an issue with the idle valve that is somehow slowly moving or something? I've tried two different (used) IAC valves, but issues were the same.
The idle valve seems to be working, as the engine dies when the air hose to the valve is pinched off.
Can I verify the function of the idle valve somehow?

I've adjusted the TPS to spec numerous times without success.
I also cleaned and replaced some other parts (intake manifold gasket, some vacuum hoses, cleaned throttle body + new gasket, replaced power stage etc.).

Any input is appreciated. Many thanks!

(ignore the lights staying on, that was when the exciter circuit was not working)


It is usually a little bit more pronounced than that - this was after only like 4-5 minutes of driving.
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Old 01-03-2020, 01:04 PM   #2
mocambique-amazone
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Did you adjust the minimum idle speed to 480-520 U/min (rpm) ? (not the TPS)
After a proper adjustment you have to adjust the TPS again.
If the minimum idle speed ist too low the probs you describe are the result.

good luck, Kay
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Old 01-04-2020, 12:22 PM   #3
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How do I set this? With the IAC valve hose pinched off?
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Old 01-04-2020, 12:53 PM   #4
mocambique-amazone
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Yes
You have to adjust the TPS again after this.

There is a manual online, I will search this again.
Good luck , Kay
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Old 01-04-2020, 12:56 PM   #5
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IIRC :
https://www.volvoclub.org.uk/faq/FAQ...linjection.pdf


(can't open a pdf on my mobile)
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Old 01-04-2020, 02:33 PM   #6
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Thanks Kay, I looked at the FAQ after your tip but it didn't say to pinch the hose off. Just wanted to be sure and I don't know how you would set it otherwise.
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