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95 850 Rough idle, needs gas

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

ebbie
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95 850 Rough idle, needs gas

Post by ebbie » Wed Feb 12, 2020 10:30 am

Hello everyone, I'm new here. :)

The problem:
My 850 has this problem where I need to press on the gas pedal in order for it to start and to idle smoothly. If I don't give it gas when it's a cold startup, it immediately stalls. And after starting it, I have to drive around for a couple of minutes before I can step off the gas without it stalling (e.g. by a stop sign or slowing down for a turn).

When the car has warmed up enough (usually just after a couple of minutes) it runs without stalling but it has a rough idle, like it vibrates a lot. If I turn it off and on again it starts fine, it just has that rough idle.

Here's a video I took (you need sound to hear the differences) -

It's quite annoying, and embarrassingly enough I've had it like this for maybe a year without dealing with it (I've even developed a technique where I use the handbrake so I can keep my foot on the gas while I shift gears when driving out of parkings).

Obviously, I know something is wrong with my car since this never was a problem before it started about a year ago.

What I've done:
I read somewhere about cleaning out the idle air control valve, throttle body and MAF. I think my car doesn't have a MAF but some air temperature sensor instead (a black and blue plug), and I sprayed that with electronic cleaner. I took the IAC out and cleaned it the best I could with some brake cleaner. I didn't take the throttle body out cause I would need a new gasket then, so I just tried to clean it from outside. I also cleaned the flame trap, cause the air hose to the throttle body was really nasty. But nothing changed.

Codes:
A2 111
A3 111
A7 122 - Temp. sensor interval too long

B1 145 - Faulty signal from function selector switch + 418 No control signal to blower fan power stage
B2 122 - Speed has not exceeded 22mph or no speed signal
B5 111

Those are the only codes I got for now. I couldn't get a signal for B6, and I don't think I had anything connected to the rest of the holes.

Anyway I'm assuming the most important one here is the "temp sensor interval too long", and I did notice that the coolant was just above the MIN sign and the temp gauge was a little under 3 O'clock, so a bit lower than normal. But I just noticed that after cleaning the IAC etc... And it felt a bit sluggish when accelerating, though I don't know if that's related.

So, I doubt that the temp could be causing the car to act this way.. Or could it? What I don't understand is why the car won't start without gas when it's cold, but once it's warmed up it's not necessary. And why is the idle so low?

Any ideas on what I can do to narrow down the problem, that doesn't mean spending lots of money on different parts etc?

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Re: 95 850 Rough idle, needs gas

Post by RickHaleParker » Wed Feb 12, 2020 7:17 pm

Pushing down on the accelerator does not give the engine more gas, it gives it more Air. The fuel is then calculated and injected.

If the temperature is not read correctly, the injected fuel will be miscalculated.
Check the wiring on the Engine temperature sensor for shorts, opens and poor/dirty connections.

Other possibilities are Barometric pressure sensor and Ambient temperature sensor.
Does the Ambient temperature on the dash match the actual Ambient temperature?
Platform: P80 1998 C70, B5234T3, 16T, AW50-42, Bosch Motronic 4.4, Special Edition package, Plant: Uddevalla Sweden.

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Platform P2 2005 XC90 T6 Executive, B6294T, 4T65 AWD, Bosch Motronic 7.0,
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Re: 95 850 Rough idle, needs gas

Post by jreed » Thu Feb 13, 2020 5:36 am

At about 1 min in on the video, it looks like the temperature indicated on the dash is low for a car that has been running an hour. I would agree with RHP above that the engine coolant temperature sensor, wiring or connector has failed and is reporting excessively high resistance, telling the computer that the engine is much colder than it really is.
1997 855 GLT (Light Pressure Turbo) still going strong. Previous: 1986 240 GL rusted out in '06, 1985 Saab 900T rusted out in '95, 1975 Saab 99 rusted out in '95, 1973 Saab 99 rusted out in '94

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Re: 95 850 Rough idle, needs gas

Post by ebbie » Thu Feb 13, 2020 10:23 am

Thanks for the replies! Shows how little I know about cars huh.

I checked the ect sensor's wires and the connection, both ends of the connection and the wires look fine to me. I didn't take it apart though, cause I didn't have the right tools and when I loosened the hose, coolant started dripping everywhere (should have read about that before doing it). So now I'm even lower on coolant and will have to buy that.

I checked with a multimeter the ect sensor's contact and it read 4.22 ohm set at 20k Ohm. The car was off and the temperature was maybe 10C. I have no clue if that's any help?

About the other sensors, where do I find them? I would say the ambient temperature that's showing on my dash is pretty accurate. I haven't measured it though but judging by the weather conditions and my own opinion it seems to fit.

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Re: 95 850 Rough idle, needs gas

Post by mecheng » Thu Feb 13, 2020 10:46 am

I agree, that it is likely ECT, they have a finite life and sometimes the connector gets corroded.
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Re: 95 850 Rough idle, needs gas

Post by abscate » Thu Feb 13, 2020 2:16 pm

ebbie wrote:
Thu Feb 13, 2020 10:23 am
Thanks for the replies! Shows how little I know about cars huh.

I checked the ect sensor's wires and the connection, both ends of the connection and the wires look fine to me. I didn't take it apart though, cause I didn't have the right tools and when I loosened the hose, coolant started dripping everywhere (should have read about that before doing it). So now I'm even lower on coolant and will have to buy that.

I checked with a multimeter the ect sensor's contact and it read 4.22 ohm set at 20k Ohm. The car was off and the temperature was maybe 10C. I have no clue if that's any help?

About the other sensors, where do I find them? I would say the ambient temperature that's showing on my dash is pretty accurate. I haven't measured it though but judging by the weather conditions and my own opinion it seems to fit.
Temperature chart here for the ECT

viewtopic.php?f=35&t=57678&start=20#p427305
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Re: 95 850 Rough idle, needs gas

Post by RickHaleParker » Thu Feb 13, 2020 2:21 pm

ebbie wrote:
Thu Feb 13, 2020 10:23 am
I checked with a multimeter the ect sensor's contact and it read 4.22 ohm set at 20k Ohm. The car was off and the temperature was maybe 10C. I have no clue if that's any help?
4.22 Ω or 4.22 KΩ?
Is that is sensor only or sensor + wiring?

Engine temperature sensor:
Temperature : °C (°F) / Resistance : Ω
0 °C (32 °F) / 7300 Ω
20 °C (68 °F) / 2800 Ω
40 °C (104 °F) / 1200 Ω
80 °C (176 °F) / 300 Ω
100 °C (212 °F) / 150 Ω
850ECTpdf.png
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Last edited by RickHaleParker on Thu Feb 13, 2020 3:28 pm, edited 1 time in total.
Platform: P80 1998 C70, B5234T3, 16T, AW50-42, Bosch Motronic 4.4, Special Edition package, Plant: Uddevalla Sweden.

Platform: X40 (Nedcar) 2003 S40, B4204T3, 14T twin scroll AW55-50/51SN, Siemens EMS 2000. Plant: Born Netherlands.

Platform P2 2005 XC90 T6 Executive, B6294T, 4T65 AWD, Bosch Motronic 7.0,
Plant Torslanda Sweden.
----------------------------------------------------------------
1997 S90, B6304S, AW30-42, Bosch Motronic 4.4 - Sold

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Re: 95 850 Rough idle, needs gas

Post by ebbie » Thu Feb 13, 2020 3:13 pm

The wire coming out of the sensor. I disconnected it and checked the ohm at the contact to the sensor, where the picture shows.

I had my multimeter set to 20K, so if I understood it right (after googling) my reading of 4.22 makes it 4220 ohms? The temperature was around 10C, and according to that chart abscate linked to, my resistance is too high? Almost double that it should be.. How important is the voltage reading? And checking it at various temperatures?
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Re: 95 850 Rough idle, needs gas

Post by RickHaleParker » Thu Feb 13, 2020 3:37 pm

Abscate's chart is for a 1999. The ones I posted are for a 1995. For a 1995 4220 Ω @ 10 °C is correct.

What is the resistance across the wiring harness when it is disconnected from the sensor?

A lot of things changed in 1999 ....
Platform: P80 1998 C70, B5234T3, 16T, AW50-42, Bosch Motronic 4.4, Special Edition package, Plant: Uddevalla Sweden.

Platform: X40 (Nedcar) 2003 S40, B4204T3, 14T twin scroll AW55-50/51SN, Siemens EMS 2000. Plant: Born Netherlands.

Platform P2 2005 XC90 T6 Executive, B6294T, 4T65 AWD, Bosch Motronic 7.0,
Plant Torslanda Sweden.
----------------------------------------------------------------
1997 S90, B6304S, AW30-42, Bosch Motronic 4.4 - Sold

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Re: 95 850 Rough idle, needs gas

Post by ebbie » Thu Feb 13, 2020 4:00 pm

Oh well that's good news then! I'm not sure what you mean by wiring harness, you mean the part that plugs into the one in the picture? If so, it was 4.38 so 4380 ohms when I checked.

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