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1999 V70T5M56 Poor cold idle troubleshooting Topic is solved

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70

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abscate
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Re: 1999 V70T5M56 Poor cold idle troubleshooting

Post by abscate » Fri Mar 30, 2018 10:54 am

The only rationale I can come up with for the warm fix is that when the car goes closed loop on ECU, the extra air leaking in is compensated for by the trim. This makes smooth performance and idle. Im really surprised I wasnt tripping P0171 trim codes from this bad hose.
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Re: 1999 V70T5M56 Poor cold idle troubleshooting

Post by wizechatmgr » Fri Mar 30, 2018 4:55 pm

Better luck next leak? =p
Wisdom requires knowledge as a prerequisite, but knowledge can be developed due to a lack of wisdom.
In order to learn how to fix something, you must first learn how to break it.
1999 V70 XC AWD - ~183k miles

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abscate
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Re: 1999 V70T5M56 Poor cold idle troubleshooting

Post by abscate » Sun Apr 01, 2018 5:37 am

And, how did this vacuum leak suddenly cure itself? Did they hose get sucked onto itself and close off?

Sounds crazy
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Re: 1999 V70T5M56 Poor cold idle troubleshooting

Post by abscate » Sat Apr 07, 2018 4:15 am

Couple of clean up items

1 we bitch about these cars but the engine management system is robust. I had a 5mm intake manifold leak directly Into the manifold at cylinder 3 but got part time cold running roughness, good Power, good fuel economy, and no codes.

2 on reflection , there was a slight flutter on running to closed throttle (think townstop sign) that I see now gone. Just on a whim, I pulled the hose on the warmed up car and it’s was back. This is probably a good marker of a small leak, a slight flutter of revs between 850-1050 on run down in gear. You slush box guys might not get this as your overrun characteristics are different, that’s why manuals rule.

I may have seen a bump in highway mpg, too early to tell. At 70mph I am getting 27 reported vs 25.5 before
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index [1999 V70 T5 vacuum hose diagram HPT M56]

Post by abscate » Sun Sep 08, 2019 4:38 am

Upthread a drawn diagram of the vacuum hose system on the T5 with hose sizes
abscate wrote: ↑
Thu Mar 29, 2018 4:24 am
...and my intuition was correct. πŸ˜€

I did a VAT inspection of the hoses, found nothing, so I removed the ones I could not see buried under the intake manifold and...obvious check valve fault.....πŸ˜›πŸ˜›πŸ˜›πŸ˜›

DFBCA04B-BE9B-457B-8625-E44288CA0EED.jpeg3F2B67D7-8608-447A-A986-C4EA10ABB4B2.jpegC5961B4F-8E75-44B7-9EAF-5DACFEC794C1.jpeg75457B9F-3449-48E1-A252-E5BC5D942724.jpeg
Empty Nester
A Captain in a Sea of Estrogen
1999-V70-T5M56 2005-V70-M56 1999-S70 VW T4 BMW
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Re: 1999 V70T5M56 Poor cold idle troubleshooting

Post by abscate » Sat Jan 11, 2020 11:31 am

My brain solved the mystery of the sudden click and clearing of the rough idle problem while I was watching first half of LIV TOT today

This is a VVT car, exhaust

On cold start, Volvo plays with the exhaust valve timing to push flame into the exhaust to clean up the cold start fuel. This also kills the manifold vacuum.

After a bit, click, exhaust VVT changes to warm mode and Presto, vacuum back to normal.
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