My '97 850 has 200,000 miles and is in excellent condition, all maintenance performed on schedule.

6 months ago it started (occassionally) running rough after warm up, usually about an hour into a long highway trip. It acts like it's too rich, smokes from the exhaust, the engine stumbles but will continue to run on the highway, but if I pull off and stop the engine will die. Restarting requires full gas and a well charged battery as it does not want to restart.

If I can pull up to a gas pump, shut down, and fill the tank, the problem goes away immediately.

This problem is intermittent , never occurs when it's cold, always after about an hour of running, and always is cured with a tank fill up. It does not seem to be associated with gas tank level, can happen at 3/4 or 1/4.

The dealer has experienced the problem (had to leave it for 2 weeks), but cannot make it reappear. They suspect a fuel condition and replaced the fuel pump relay. I just got it back, so I don't know if this will cure it.

Other posts suggest that the thermostat / ECT sensor replacement might help.

Comments ???

Bill

 

Any codes stored in the ECU?

 

no codes are showing up ....the 97 850 apparently does not store past code errors....only what is happening now.

 

I have a hunch it is a bad Mass Flow sensor. I have seen a couple of cars do this before.

 

Thanks....I am going to try a local garage known to be good on Volvos I will suggest the MFS....any idea on cost to replace ?

Bill

 

The sensors are pretty expensive. Maybe they will have a used one you can try to make sure that is the problem.