Folks,

Last week my wife's 850 wagon started - what she described as a surge.

Finally got to looking at it Saturday, and what I find is:

1. Miss at idle.. rough idle and can hear the miss at the tailpipe
2. Miss when off-idle under load. Feels like a surge, but is really a miss.
3. Gas mileage appears awful - something like 12 MPG.. normally closer to
20-22 MPG.

So - I gave it a complete tuneup.. new plugs, new cap/rotor, airfilter, cleaned the flame trap (what a PITA to get to..)

Not really any better.

But - one clue - if I unplug the AMM - the idle smooths right out and the engine smooths out above idle.

I've seen and experienced AMM failures that caused the car to not continue running unless the AMM was unplugged (my son's '86 240..)- but in searching the brickboard, I can't find any references to rough running.

Ideas?

TIA!

Don Eilenberger

If you find anything let me know...I am experiencing the same problem. Everything was fine until I put in a new tranny, now I have the exact problem you are describing.

Thanks

Dave

Dave,

Thanks for tweeking me..

I should have posted the outcome here. The AMM was not the cause (an expensive lesson in troubleshooting by replacing parts, something I try to avoid doing..)

What was the cause was a vacuum line that is buried under the left-bottom of the intake manifold. Thanks to a good private independent, he listened to what I'd done, looked at the car, felt around underneath and plugged the leak with his thumb. The idle smoothed right out. Since he only works on Volvo's I guess he has seen this one before. Strangely - all the other vacuum hoses and elbows on the engine looked just perfect.

He replaced it for me in about 15 minutes.

So - the lesson is - make really certain it's not a vacuum leak before jumping to a $200 AMM (which will be on ebay shortly since I reinstalled the original one..)

Best,

Don

Have you replaced the ignition coil? After a lot of miles/age, when replacing all the other ign. parts, sometimes the coil reacts poorly to the suddenly more efficient wires/cap/rotor.

Happened to me on my 850, and I switched the ign coil from my c70 and it ran great, so I replaced the coil. There's a lot of juice to run a modern ign system.

Jeffery..

Nope. I think the point that is missed is that if I unplug the Air-Mass-Meter (AMM - known on other cars as an Mass-AirFlow-Meter, MAF) - the problem goes away. That sorta points away from the coil or the fuel pressure regulator.

We'll know shortly - I have a new AMM on the way (~$181.00)

Thanks!

Don

Hi

Pull off the vacuum hose that goes to the Fuel Pressure Regulator (above the inlet manifold and under the fuel rail), IF it leaks a few drops of fuel then it needs replacing. Typical for your symptoms.

Check also vaccuum leaks.

Matt 93 850 GLT auto

By the way, any codes??
M

As I think I mentioned - haven't checked 'cause I don't own a code reader and haven't gotten it to the friend who has one.. plus I know there will be an AMM code since I disconnected it for testing and ran the engine.

Best and thanks.. will check the FPR when I get home..