Hello BB:

My wife's 2002 V70/T2.4 wagon (250K miles) RPM has started surging recently when engine is cold. As an example, now that the weather is colder, it does take a bit longer for the engine to start, then the RPM surges between 500 - 1100 RPM for a few minutes, then the RPM eventually settles at around 700-800 RPM when engine gets warmer. It does NOT stall and it does NOT appear to surge after shifting from "P" to "D", even when engine is cold.

We recently had both O2 sensors replaced, but other than that there was no related repair or maintenance performed in the last year. I think the fuel filter may need to be replaced (... not sure when I had this done last). I have not checked codes yet (but the check engine light is NOT on).

Lastly, Volvo did replace the Electronic Throttle Control Module about two years ago ($$$$$) due to a known issue for these vintage cars. At the time, the symptoms were different though: the RPM started surging under ALL conditions (even higher RPM when engine was warm), sometimes even stalling the engine, and the car eventually "died" and never started up again (had to have it towed to the dealer). 'Hope that is not the problem again!

'Any thoughts?

Thanks.

Bernie

Hello BB:

Happy 4th of July weekend. Just wanted to provide an update on the issue of surging RPM at idle. As some of you had suggested, it appears to be related to some "BAD" vacuum hoses which I ended up replacing with the Volvo kit. Thanks to all for your helpful suggestions.

Bernie

Hi Bernie,

Your post indicated a vacuum leak that you found OK.
Hopefully you replaced All of the geriatric vacuum lines and elbows.

You also had problem #2: maybe a faulty TCM connector.

Please post what you did to resolve the TCM issue?

Technical forums really suck if all you have are people posing problems
without posting any solutions.

Cheers, Bill

Hi Bill:

Have not yet checked TCM connector, but did buy ECU removal tool, and reseated ECU. Also, car just started cutting out at low RPM again this afternoon. Thinking of throwing a new MAF sensor at it and cleaning all connections from battery forward. This is fun!

Cheers.

Bernie

Hello BB:

Update as of Jul. 18th. I replaced all bad vacuum hoses, and checked/cleaned all electrical connections. Car is still occasionally stalling at low rpm. Noticed oil by the oil cap, performed glove test when engine at temp. Glove inflates ... do I need to have PCV system checked? Is this big $$$?

Thanks.

Bernie (aka BZ)

Bernie,

As Bill suggested, a good starting place is to pull any OBD codes you might have. If you don’t have a scanner some Auto Parts stores used to read your codes for free. Don’t know if that is still the case?? Definitely clean your engine grounds. Be careful if you clean the connectors. Don’t replace the MAF (also known as an AMM). Instead, if you want to try something, you could buy a MAF cleaner and clean the connector plug. Be especially careful not to damage any of the connector pins.

Jim
--
Will I buy another Volvo??? We'll see....

Hi Bernie,

AKA BZ?

Don't throw parts before diagnosis.

Get your OBD codes first, post back.

Bill

Hi Bill:

Yep, BZ is my nickname. I don't get any codes (just a message saying "engine service required"). I was going to check electrical connections next, but was also looking to throw a new MAF sensor at it (until I found out how much they are). Maybe there are other vacuum lines I should check (other than the ones that came in the Volvo kit)?

Maybe I should apply dielectric grease to the ECM pins?

Any other thoughts? I'm surprised I have never gotten any codes on this issue - maybe that's a hint?

Thanks.

Bernie

Hi Bernie,

Connectors can be a failure point.
Disconnect the battery before unplugging ECU's.
Use a light smear of dielectric silicone to deter oxidation/corrosion.

I suggested before that you replace all of your old crappy vacuum lines and
elbows to be proactive and save yourself some headaches.

Study this article: https://www.wikihow.com/Find-a-Vacuum-Leak

Post back with details of what worked for you.

Bill

Hi,

I don’t know anything about these cars first of all but I cannot help wanting to comment about the vacuum lines either.
My 240’s use vacuum to do similar tasks but simpler.

You stated that you checked the “turbo boost systems vacuum lines.”

I think you need to forget that turbo stuff for now.
It seems to me a surge in idling has nothing to do with the boost responses or any pressure sensor.
The turbo is dead until it gets exhaust gasses to spin it.
As far as the computer goes it has finite perimeters to follow to control the turbo.

That system probably relies on a computer inputs like the RPMs and type load present from the transmission sensors.
It calculates the needed amounts of idle air or boost depending on what gear the transmission is in and the throttle position from the driver.
The throttle position is about the only other input that comes from the driver.
No CEL means nothing emissions wise is out of line far enough.
Excessive idle speed isn’t watched in the codes as its a naturally man made variable.

The vacuum lines that the other posters are recommending for you to check out are probably everywhere else on the car.
I suggest that you isolate different parts of those areas that use vacuum.
Figure in the cabin vent or heating controls, any line going down to the transmission or over to the power brake booster.
Especially, if it’s warming up with a foot on the brakes.
Common place to happen on a car that not dependably smooth.
Hopefully it’s not bad enough to cause the cell phone to jump out.🙄

The engine is the vacuum source and you work out from there towards any branches until something changes.
It’s not all that hard to pinch off lines but keeping your methods simple take practice.
This helps to narrow things down to an area and how it’s getting more air to allow the engine to rev up in the first place.

The scientific way is to one thing at a time and look for results and keep working outwardly to find a defective line or component.
Something is not working proper or is trying to correct another thing that isn’t.
A misfire on a cylinder will cause minimal idle fluctuations but a leaner condition from excessive air mimics other problems.

How long since an ignition tuneup?
You haven’t been on the BRICKBOARD if the last seen is right on the first post.
The engine is getting air it’s not supposed too.

Suggest you to Use the KISS method as much as possible.
KEEP IT SIMPLE STUPID.

There should be a vacuum routing diagram on the car underneath the hood on newer cars along with other labels. That is, unless the rules have changed and they do not disclose that information to make you buy manuals or to get the car serviced.

AS I mentioned earlier, the main input to any computer is the drivers foot.
In being such an item that uses a variable scale throttle control to talk to a computer. They have thin internals that wear out the faster or are more susceptible to getting fouled up by grunge or engine cleaners.
I don’t know what a Throttle Control Module is but if that’s your problem you don’t want that specific OEM one again.
The module name is fancier for more dollars.

I see from your dollar signs sprinkled here and there it’s big worry’s.
If I were you I would always request my old part, before leaving. I don’t know I’m that way but now in California it’s a law if you request them you better get them.
Just don’t mention it right up front because they have to find the problem and then produce the bad part.
If I was spending big bucks on service I would mark my cars components in an inconspicuous way.
By marking a part with a tiny scratch of a file, dab of paint or a inconspicuous ding with a center punch.
The BRICKBOARD is full of guys that take old parts apart to see what failed and how they work!
There’s one last thing, that the part can do for you, teach you something.

If you think I’m kidding then you haven’t taken a fuel injection in a city college several years ago.
The town’s mechanics talked shop during class breaks about how they get spare testing parts.
They hide them in their super size tool boxes.
It helps them to beat down the service times given to do a certain task.
There’s one to read the codes or do diagnostics with a machine for a print out but when they have already seen the symptoms before ….guess?
The customers never knows the difference if it was something simple that they cannot technically charge for.
So, they get a used spare testing part.
Customers car is fixed, dealer is happy and the rumble continues.
Mercedes were the most mentioned at that time for guess what, idle control boards. Now called modules.as
These varied from model to model so mechanics do what they do.
Advertisements then said, “Built like no other car in the world”. I believe they meant it too!

I changed out one on a 2002 Dodge truck for having excessive idle speed problems, that were MOST noticeable, when the vehicle engine was not loaded by the transmission.
I tracked it down by “noticing” that it would always hesitate to idle correctly or the same right after every adjustment with my foot.
The truck had a tachometer.

A new throttle sensor was $35 to $85. One being an economy one and the other was OEM.
Both were offered from the same parts house.
The decision was simple for me to get the economy one because we already had the OEM one that was failing.
An ohmmeter test helped as I remember but replacement was the final step but I tossed it after I took it apart!

It’s been about fifteen years now and the problem has not reoccured.
But then again that truck doesn’t get used as much.
My sister-in-law’s husband passed shorty before this and due to gas prices being what they are now, it sits on her place waiting to move something.
I ask occasionally and she runs it every few weeks and it’s still doing good. I figure it’s debugged!

Older vehicles still can be tougher and cheaper to maintain. Because 2000 vehicles were watching out for the “Y2K” issues that didn’t appear as much as the worriers predicted.
Manufacturers slowed down on the electronic gizmos.
But now,
For the last few years, that has “chipped” them in the butt!


Hope this gets your hands and mind into the car more often.
It’s been awhile since you worked on it. A January thread?
Hopefully others with more experience on this series can chime in.


Phil

i would checl mass air flow maybe it needs changing or go new

Hello Phil:

As B.B. mentioned, thank you for the very detailed response. I have more symptoms to add:

About two-three weeks ago the P0234 code popped up. After doing a bit of research, I checked vacuum for vacuum leaks, replaced boost pressure valve and pressure sensor, and had the car running ok for a week until the P0234 code popped back up and symptoms came back. A few days later, the car would start, but RPM control was impossible and engine would stall out within seconds (no more codes). These symptoms are exactly the same I had four years ago when I had the dealer replace the throttle control module ($1,200). Is it possible that these modules are still defective, and don't last?

I am taking the car to the dealer on Thursday (5/11). Any input from my fellow BB experts would be appreciated by then.

Thanks.

Bernie

Hi,

From what I reading or you’re saying you think the modules have a short term life expectancy.
I gather that this car is over twenty years old.

Do you have any idea how many of these have been charged over its lifetime.
I haven’t read if the module ever failed before the last four years.
With that idea I would say last 15 years, so it should be very unlikely to have failed this soon.

The dealership should be able to know what the history is from maintenance records or since they sold you that part before they had better be very careful in the diagnostics.
In their minds they would rather sell you another Volvo but as it has been written “we will shall see?”

That to me sounds like it was one of the most expensive parts on that car but …. Like I said I know nothing of these cars except they have larger sparkle in the wheels.😳
Only a major snap in the driveline, engine or transmission, could be worse for many people.
Then again your car was the first ones of a new breed that broke from the heritage of the 850s.

It might have been the age of turmoil in Volvo but the earliest 2000+ FWDs had some good years.
From what I hear their not nearly as bad as the newest cars of today.
I heard they have “scheduled maintenance” night mares and lots of small nuisances.
The bugs are in there to be found with patience and $$$ at a time. Something sold them in the first place but love has to grow in the owners.


Like is said earlier and like BB is saying it appears to be a throttle issue or at least an idle control valve for my two cents.
The computer has lost control through communication or a small component.
It’s not responding. The Codes can be very generic when it comes to emissions type CELIghts.
The car seems capable of still doing good as we are looking 👀 for a cause for the hiccups! 🫢

IMHO, Both of these can be affected by a mass air flow sensor of some kind along the way.
B B could add in for you to find your sensor and clean the connector pins on it too.
2002 is not all that far from my early 1990’ 240s & later 900s.
It just took sorting through observations of what and when. Puzzles are entertaining believe it or not.

Maybe Volvo’s idea of dropping the combustion engines is saying “enough on that horse” as China is starting to boil down onto electric vehicles. Several different vehicles are headed world wide.
The killer is going to be the battery proliferation problems.

Taking it to a dealer, who sells new ones, does not sound to me to be the greatest show on earth.
There is another thread on here about a wrong fitting front axle on a 2006 FWD “R”model.
That’s got to be some wonderment?

There is fellow recommended in the thread that has done a lot of YouTube videos on these cars.
He may have covered one of your quirks?

Do some surfing in and around that new “modern style university” for symptoms.

Phil

Hi Phil,

One thing worth mentioning is buried here and there in Volvo manuals
and easily overlooked:

"Disconnect the battery before doing any welding on your car."
This is to help prevent damage to ECU's.

You have to wonder if any muffler shops do that when they do their welding.

Cheers, Bill

Hello B.B. and Phil:

Thank you for the additional feedback. I had 15 minutes to look into the ECU and TCM compartment (before work) Unfortunately, you need a special tool to unlatch the computers and re-seat them. But by pushing and wiggling both modules, now the car will run - hopefully long enough to drive it to the dealer instead of having it towed.

I fully trust my dealer (he's worked on our Volvos for 20+ years), and will ask him to re-seat the computers before he does anything else.

Thanks again.

Bernie

Hi Bernie,

I'd suggest that you take the connector apart for the Throttle control switch.
get some 90% isopropyl alcohol and a tooth brush and scrub both male and female
connectors until they're shiny squeaky clean. Then blow out with compressed air. Then apply a very small amount of dielectric silicone or maybe CRC spray silicone that you can pick up at Walmart, then reassemble.

Service your ground wires, especially the two signal grounds for the ECU's on the intake manifold. Clean them, grease with never seez, and reassemble.

Reset the codes and see what happens.

Post back with your results.

Bill

Hi Bill:

It looks like the issue was related to a poor connection of the main ECM. After wiggling (pulling and pushing on) the ECM moule a few times (since I do not have the tool to remove it), the P0234 code and associated symptoms (including stalling and loss of throttle control) have disappeared to the point where the dealer said he cannot replicate the problem either. But I will order the ECM removal tool ($20) and pull out the ECM to inspect the terminals (and clean if needed).

Thanks again for your help.

Bernie

Hi Bernie,

Make sure you have any needed radio codes.
Be certain to disconnect your battery before unplugging any ECU.
Then be extra prudent, wait ten minutes like they say with air bag service
before unplugging ECU's.

When you get the connector apart look carefully at the pins to see
if any any look spread open, or there's signs of corrosion.
Volvo warns regarding ECUs to avoid probing the ends of those pins to avoid
damage. Instead there are access holes on the side to probe the female pins safely.

Post back with your findings.

Bill

Hi Phil,

I like your detailed posts.
I'll thank you in BZ's behalf.
Check back at the end of August for a possible reply.

Cheers, Bill

We had the same problem with our 1972 Volkswagen 411.

The owner's manual even told us which hose became disconnected!

I agree, check your hoses.

Finally got back to checking vacuum leaks on the turbo boost system (P0234 diagnostic code) per this link on YouTube:

https://www.youtube.com/watch?v=0rJJQz46Ae8

But vacuum gage showed NO leaks. What's the next step? Replacing turbo pressure sensor? Any other parts to check (or replace) before taking car to the dealer ($$$)?

Thanks.

Bernie

Hi Bernie,

The first thing I'd do is look for vacuum leaks.

After 20 years it might be smart to replace ALL of the vacuum lines and elbows since they murder the engine management of all cars when they crap out from old age.

Don't assume any garage will do anything like this without asking for it.

Bill

Finally got back to checking vacuum leaks on the turbo boost system (P0234 diagnostic code) per this link on YouTube:

https://www.youtube.com/watch?v=0rJJQz46Ae8

But vacuum gage showed NO leaks. What's the next step? Replacing turbo pressure sensor? Any other parts to check (or replace) before taking car to the dealer ($$$)?

Thanks.

Bernie