I've got a '95 850 GLT with 109,000. It's got some symptoms similar to this guy's: https://volvoforums.com/m_94710/tm.htm. The rpms waver between 500 and 1000 and it sometimes stalls when idling. It doesn't stall regularly, but the rpm issue happens on a daily basis. There are times when it sounds like something catches and the pitch of the cars idle goes up. Then everything is fine.

However, when the car fussy and in gear, it hesitates to accelerate. The rpms sometimes shoot up, but the transmission doesn't react. It is like the engine is revving in park or neutral. In gear, if I push the accelerator to the floor, the car speeds up 5 mph. By pumping the gas pedal I can cruise 60 on the freeway.

The Check Engine light is on because of two faulty oxygen sensors, the mechanic has repeatedly told me are no big deal.
Fuel filter, spark plugs, idle control motor have recently been changed.
I have twice taken it to a trusted mechanic. Once they couldn't replicate the problem. Second time they changed what I listed, and the car experienced a temporary fix.

P.S. Unlike the guy I linked, it has no problem starting.
The problem has been happening since October, there have been good spells and bad spells with no pattern in regard to fuel level or outside temperature.

Any scalpel-like insights?

 

Replace the O2 sensors first then takeit from there.

 

The link you posted didn't work for me but I'm almost positive I'm the one who you're referring to. I had all the problems you're having and it took me about $600 to find out what the problem was.

https://volvoforums.com/m_94710/tm.htm

My problem was the mass air flow sensor. The dealer had to check readings on the individual sensors (the independent Volvo mechanics in town didn't have the equipment to do this so I had to take it to the dealer). They replaced the mass air flow sensor and the air filter (wasn't related to the problem, but it was dirty). It cost about $420, but that included two hours of diagnostics at $98 an hour.

Hope this helps!

 

See if you've missed something in the list; see my 2nd reply from top for tune-up items.

https://volvoforums.com/m_48928/tm.htm

Also, when you service your car, always insist on OEM parts. Many imports do not like to be treated with non-OEM parts.


JPN

 

Listen to Tech and JPN....They will not steer you wrong. IF it was me, I would do (in order) OEM spark plugs (and wires) O2 Sensors (and reset to check engine light to see if there are any other codes stored) then the MAF.

Keep us posted

 

I had the mechanics replace the "bad but not problematic" oxygen sensor and VIOLA! the problem is gone! A month has passed and the car is healthy. Next I will be looking into the malfunctioning sunroof and squirters of windshield solvent.

Thanks for the guidance, you guys where dead on.