1994 Volvo 940, Bosch. 257,000 miles.

Recently my car has developed a high idle--1400 rpm. It hangs there after a drive.

Simultaneously, the speedometer has stopped working. Weirdly, the odometer is putting on 10x the miles actually driven.

My mechanic, an experienced Volvo tech, is trying to work through the issues. He had replaced the idle air control valve, which (he says) has addressed the idle issue.

He is planning to see if the voltage regulator (an original part) is defective, and putting out too much voltage, thereby affecting the speedometer. If not, he is planning to have the speedometer rebuilt. He is not certain he is going to be able to solve these issues.

I have trouble believing that these issues are not somehow related.

My questions are: 1. Anybody have any insight into these issues occurring simultaneously? and 2., If he cannot solve these issues, anybody know any good Volvo shops in the greater Los Angeles area who perhaps can?

Thanks!

Off the top of my head I don't see how these issues are related.

1) A high idle as you describe is often associated with a failing block temp sensor. The idle may or may not be too high to start with a cold engine and continue to rise as the engine warms. I've seen idle speeds listed here going as high as 1800 rpm as the engine warms, with closer to 1300 being more common when the problem begins. Inspect the wiring under the intake manifold (the rearmost sensor). The resistance can be checked against specs. If you dig around there are graphs you can use, just make sure they're for the correct temp sensor. From the 700/900 Pocket Data Booklet, for the common Bosch sensor p/n 0280130-032 used in the LH injections systems, as a quick check you want to see
8.26-10.56K Ohms at a sub-freezing -10 degC (14 degF)
2.28-2.72K Ohms at room temperature 20 degC (68 degf), and
290-364 Ohms with a well warmed engine at 80 degC (176 degF)

But first, make sure the ECU knows it's supposed to be idling when the throttle is released. Check the TPS for the click (and if needed using the OBD diagnostic socket test). Insert a fold of 20 bond paper at the throttle stop screw and it should still click on opening the throttle otherwise it's set too close on the hairy edge. Also make sure the IAC valve isn't sticky and that it can be controlled by the ECU. Tap solidly on the IAC with the end of a wood stick while the engine is idling high to make sure it doesn't change -the idle will change and become closer to normal if the IAC is sticking/dirty/worn. If the IAC has failed there's also an OBD diagnostic test you can use to verify operation of the IAC (the tic-toc test). See the OBD section of the FAQ here.

2) For the speedometer, the common issues with 940 speedometers are exactly as Art says. A quick inspection under the rear will tell you if the speed sensor wiring on the diff is damaged or broken. If not then it's likely the speedometer itself. As he noted, it's in the FAQ. That would also explain while the odometer is still working, albeit it reading incorrectly. Hopefully the shop will be able to put it right for not too much money.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

The high idle after driving is related to the speedometer quitting. You'll find it has set a DTC 311 for loss of VSS. The simplest cause of the sudden onset is often the wiring at the rear axle differential, where the vehicle speed sensor is. Your 900 has the same sensor as shown here on a 240.

But with the 900 comes more difficult issues in the speedometer itself, as the corrosion from leaky electrolytic capacitors destroys circuit foils. See the 7/9 FAQ. Have your mechanic see the FAQ list.






--
Art Benstein near Baltimore

“Expertise in one field does not carry over into other fields. But experts often think so. The narrower their field of knowledge the more likely they are to think so.” – Robert A. Heinlein

Hi Art,

He can check for OBD codes to confirm.
He says that the odometer is still working but upset and over-recording X 10.
That suggests his sensor may be OK and the problem is at the instrument cluster.
It shouldn't take long to check out the instrument cluster cap and connections.

Have you tried LED headlights in your 240's?

Best regards, Bill

Thanks, gentlemen. I just spoke with the mechanic. There were no codes. The cluster has been sent out to a specialist for a rebuild. The idle is still acting up.

Art, can you indicate how the failure of the speedo/cluster can affect the idle? Thanks.

Thanks, gentlemen. I just spoke with the mechanic. There were no codes. The cluster has been sent out to a specialist for a rebuild. The idle is still acting up.

Art, can you indicate how the failure of the speedo/cluster can affect the idle? Thanks.

Thanks, gentlemen. I just spoke with the mechanic. There were no codes. The cluster has been sent out to a specialist for a rebuild. The idle is still acting up.

Art, can you indicate how the failure of the speedo/cluster can affect the idle? Thanks.

The 311 code won't be set until you've reached and sustained RPM and load minimums the ECU is programmed to deem as driving, not idling in your driveway. Then, without the VSS input from the speedometer, the idle valve no longer regulates idle speed. If you shut the car off and start it again, idle will be regulated until it thinks you're driving again. When driving, the idle air path is opened up so, as the service literature explains "the development of unnecessarily high negative pressure in the intake manifold when the throttle shutter closes suddenly during deceleration."

tldr: the ecu needs the speedometer signal to properly control the idle

Here's an example of the many posts questioning this behavior:

https://www.turbobricks.com/index.php?threads/volvo-940-smoke-coming-from-the-dashboard.374570/#post-6413939
--
Art Benstein near Baltimore

An elderly father asked his son if he could borrow a newspaper.

“Father, this is the 21st century,” replied the son. “I don’t waste my money on newspapers. But if you like, you can borrow my iPad.”

The spider never knew what hit it.

This is so interesting. Thanks--I have passed it onto my mechanic.

I've not worked on a 940 in almost 20 years, but I have repaired some of those Yazaki speedometers from 940s belonging to friends. This idle issue comes up every time a 2,7, or 9-series Volvo owner (with LH2.4 fuel system) figures they can drive the car without its original speedometer.

The repair of the capacitor issue can be tricky. I've documented my efforts here for both the 91-92 and the 93-94 7/9-series Yazakis.

Notes on 740/940 Volvo Speedometers

--
Art Benstein near Baltimore

Why do dogs love humans?
They don’t, they just like biscuits.

Now that I can again access this site, I really wanted to say thanks to all those who posted on this thread, but especially to Art Bernstein, who nailed the issue with the speedometer signal. I got my speedo rebuilt, and when it came back, everything worked great! My mechanic of many years says that he didnt know that, either. Thanks again, Alex

Hi Art!

Talking about what will not function properly I think the Brickboard is missing its VSS!

Very Special Subscribers! Without people to even post guts its purpose.

I have been writing my thoughts down on a whole host of things to put into private emails to you and to BB, if it kept going.
He another person at his suggestion to have as an email for in my contacts, thankfully.
I will sorely miss the comrades of the 240 gang.
Imagine the wealth of knowledge on Volvos tied up in that site?
Not just Volvos but how to diagnose and trouble shoot automobiles in general.

It has set idle for me for over a week now.
I was starting to think that it stopped circulating around the drain.
I worried that another giant sucking sound had gobbled up the Brickboard.
These are ghoulish times and it’s not a Halloween feeling.

The below is for all to pause on before the election in the USA.

Ross Perot said the giant sucking sound would happen if the old man BUSH and the Republican’s agenda got the North American FAIR Trade Agreement.
He warned about, Saying goodbye to good jobs and our country’s edge on innovative technology.
We were already suffering from Mergers and Acquisitions of retirement plans in the eighties.
Brian Willams of NBC did a special on the “fleecing of America” in the late eighties or early nineties.
M & A’s, no watch dogs and decertification of unions powers by reducing jobs within the above allowed it to happen.

Perot said it’s a two party thing all along. Smoke and mirrors of back room deals I would say today and they are the masters of “double talk”. A forked tongue as Native American said long ago!
I was fleeced out of any interest my company made on monies in their accounts that was set aside for a union agreement contract retirement.
This was before Ira’s and 401K’s


He said our politicians have never made “good deals” without strings and loopholes for contractors and other countries
What he didn’t know that it was already on a “fast track” bipartisanship bill was a gun to the taxpayer’s head. We have left the cash register open for too long.
Clinton couldn’t have stopped it and only the .COM era kept the nation’s budget and the dollar value sound in the eyes of the world.


The grotesque numbers in all the global markets are “false economic indicators.”
Not a true values of worth anymore.
They are the result of worker retirement accounts moving through the stock markets through “Holding” companies.
Using our investment gains to take back what they didn’t want you to have many years ago!

It’s what is pushing up inflation by their wholesaling every market that a consumer uses.
Food, housing, etc.
Everything is running on credit or a willingness to play along much like a Monopoly games with some sort of world order in its web of threads.
No plan, we are all just bumbling along until some primary countries “JOSTLE” the tables and more numbers crawl out of thin air!

It’s appears “legal” if your courts are considered “legit” and not turning their heads to listen.
They have nice retirement plans too.
Money and power favors snuffs out the hearing and seeing for long periods of time.
Like since human greed went into play for many centuries.
The swinging pendulum luckily works like a big club to keep things mediocre.
In the physical world of civilization … Perfect doesn’t exist but a middle or mean tolerance level of value makes it work.

Phil

Hi US Diver,

I think it's likely that the two issues are unrelated.
Maybe the sensor is OK back at the rear end differential.
You have a good chance of finding the problem by removing the instrument cluster.

4 pin connector D in the center of the cluster is for the speedo/odo.

First make sure Connector D is seated and making good connections from the connector wires to the onboard tracks with your ohmmeter.

There's an unspecified series component in the speed sensor circuit. One end tied to connector D2, surely a capacitor that may have failed open or short, or have a bad solder joint. There's no component value in the manual.

You can measure with an ohmmeter: D2 (Br-white wire) to ground
found at pin 2, at 8-pin Connector A (upper left connector looking from back)
The wire at pin 2 is Br-Gr.

Also verify the tracks of the flex card from D1 and D2 to the speedo S- and S+ connections. Bad solder connections are common on the flex card
requiring careful solder re-flow and if the bad joint is where the track goes to the other side of the flex card and back, you need to add a jumper.
There are dotted lines printed on the flex card to highlight where the jumper needs to be placed.

Give an email address and I'll send you the wiring info for the Speedo and instrument cluster that makes it easier to understand the above.

Good luck, Bill