I discovered that the 850 that I just bought has an issue. At about 3500 rpm's the engine suddenly stumbles and starts to shudder. When I drop the rpm's to 3200 it smooths back out and runs fine.
Does anyone have any idea what would cause this?

 

Being that you just got the car you should start with a full stage "0"
Including the PCV...

You should really read this thread over, it will explain alot.
https://volvoforums.com/forum/volvo-...s-s-v70s-9266/

 

What is a stage "O"?
I will give the car a full tune up but this kind of stumble seems like something over and above that.

 

Dear Phil, Stage 0 is a full tune-up. You should do cap, rotor, plugs and wires. If you notice any blowby or smoke from the dipstick tube or oil getting pushed out the oil fill cap you likely are in need of replacing the PCV system, it's spendy at around 100 bucks but it's necessary.
I'd also do the fuel filter and ad a bottle of Lucas or Chevron fuel injector cleaner. They really do work. Check the air filter and replace if in doubt of it's condition.
Also pay attention to all the vacuum lines. They get brittle with age and can split or if it's a turbo the heat can cause them to break down and sometimes even plug internally when they don't look too terrible outside. That and the preformed elbows. Over the years they lose their grip and fall off easily.

Any chance you have a check engine light ??

It's possible you have some type of spark scatter or a break down of the wires or carbon tracking under the cap that only occurs at the higher RPM under that stress and the stage 0 will cure it. If not at least you (we) know you have a solid secondary ignition set up and it's time to look deeper at a cause.

Once you have the tune up done if you still have the problem I'd recommend getting your hands on a fuel pressure gauge and see what you have for pressure in the fuel rail. Easy enough to do as it screws on.

 

You would be surprised on what will cause a stumble on these cars, a cracked vac elbow can cause egr codes... a leaking intake manifold gasket could cause a tps code with a flashing arrow...

Do you have any codes?

 

There had been a code just before I bought the car that was caused by a cracked hose. I hooked up a reader last night and there were no codes but that was at idle. The code reader reads from the memory but I might know of someone that has a reader that gets instant readings so I could hook it up and have someone watch it while I drive. The frustrating thing is that below 3200 it runs great.

 

It could be anything from old plugs to a bad coil to a jump in timing..

DO the FULL stage "0" first...
Cap,rotor, plugs(copper gapped at .025), wires, AF, FF, Injector svc, PCV, check your timiming and go from there...

 

I don't know if this could be an issue but should something be plugged into the connector on the left in this picture.

 

Lol, no, just a cap. But neither should that jump wire. Pull that wire out and let it hang until you get the cap that goes there. I have one if you would like it. Just pm me.

PS: Welcome to the site.

 

That is the diagnostic panel for reading codes. The wire shouldn't be plugged in unless you're using it to read them. It normally stores in the cover as shown in the picture of the cover in the hand. Use something to keep it covered to keep dirt and moisture out until you can get a cover for it.

 

There was a cover laying next to it. So the wire is only put in the when you read codes? Are you saying there are codes that are read at that block some how or do you step the wire through the various connections on the block and then use the code reader at the OBD11 inside?

 

Those two little panels are what every car in the world should be wired with. You can check almost any system in your car. You can even reset an air bag light with it. I know because I tripped mine by mistake and though I was going to have to pay the dealer to reset it.

What Codes You Can Get

Listed below is the information retrievable from the various connections.

• A1 Transmission
• B1 Climate Control
• A2 Fuel System
• B2 Cruise Control
• A3 ABS
• B5 SRS
• A5 TCU (Transmission Control)
• B6 Power Seat
• A6 Ignition System
• A7 Combined Instrument

How to Use the Jumpers

Normally “Check Engine Light” information will be found in A2. Put the jumper into A2 and push the black button for one second. Count the red LED light as it blinks back information, blink, blink, pause, blink, blink, blink, pause, blink, blink, is an example of the response you would receive. 2-3-2 would be the code retrieved, now push the button again for one second, again count the blinks, keep checking for codes until one of them repeats, this means you have read all the codes.
Clearing Codes on your 850

Now to clear the codes, push and hold the button for 6-7 seconds, release and as soon as the LED comes on push and hold the button for another 6-7 seconds. Now push the button for one second and read the codes again, you should get 1-1-1 (no faults).
You Must Read All Codes before Clearing

Turn the ignition off and then start the car, the check engine light should be out. It is always a good idea to check for codes, clear them and then drive the vehicle to see if they return before replacing parts. The transmission can ask the check engine light to be turned on, so if you try clearing A2 codes and they wont go away try reading the transmission (A1), clear them , and then go back to A2.


Check this out for list of the codes you'll retrieve from the panel:
http://www.matthewsvolvosite.com/read-codes-volvo-850

 

Are there any preferred brands for plugs, filters etc.
This is a really good and helpful bunch of people on this forum and thanks to everyone for helping me with this. For the last 8 years we have been driving a 1983 Mercedes diesel and although its a great car its getting to the point where there are always things to fix on a car almost 30 years old. I am looking forward to getting this Volvo going, and it has a lot more power.

 

I went through the codes the correct way this time and now I'm confused. When I had the jumper plugged into A3 I got a code 213 and that's listed as an item in A1. It says "throttle position signal to high". I don't know why this showed up in A3 but what does it mean and is this something I can adjust or how do I fix it.

 

An update, this turned out to be a main relay dropping out the fuel pump relay. Hope this helps someone else in the future.

 

I didn't respond to this because everyone has a different opinion. Best recommendation I can give you is use quality parts and they will repay you with reliability.
There have been concerns about the Fram filters leaking down and allowing a dry start and lifter noise. I experienced it myself and now don't use Fram on my Volvo. I'm running AC Delco platinum plugs and they have worked great. I do have a MSD coil firing them. A lot of guys use FCP and IPD for parts and want to stick with Volvo stuff I tend to shop local parts stores but get name brand replacements.

 

My volvo supplier uses Mann filters, which seem to work fine with my car. Air Oil and Pollen filters I get in that brand

 

Oh, and code 213 from A3 is an ABS fault, it is left rear wheel sensor, signal absent when moving off. If the ABS light is not on, I would say it has either been fixed, or started working again.