I’ve got a 1997 850, Non-Turbo, with 310,000 miles on it. We are the 2nd owners of it, it was gave to us by my mother in law (who purchased it brand new) and it has been properly maintained by Volvo dealership (including timing belt replacements). It’s a great car and I love it.

My issue is sometimes it seems to idle rough when In Drive. It does it if I’ve got my foot on the brake or if I’m going less than say 15 MPH. It does it off and on and sometimes it feels like it’s going to cut off and sputters but it doesn’t cut off. It doesn’t do it in Neutral or Park. I thought it may have been bad gas but I don’t think it’s that.

Any suggestions??

 

more likely you have a small vaccuum leak. check the vaccuum hoses for cracks (particularly at the vaccuum tree located under the throttle cable spool cover). with the engine idling, spray around with some carb cleaner on the vaccuum lines, intake tubing, fuel injectors (ie their seals). If any gets sucked in it should bump the idle. Next do a rubber glove test (ie latex surgeons glove) - with the engine idling, remove the oil fill cap cover with the glove. If it inflates like a balloon, you have positive crank case pressure (which can mess with the vaccuum) and you need to service the PCV system. Finally, when was the last time you gave it a full tune up (plugs, wires, rotor, cap). Check the wires for date codes - if they are older than 5 years, time for a refresh. PS, when it comes to plugs, go with standard copper core (Bosch, Champion or Genuine Volvo etc). Make sure they are properly gapped (I think its .028). Also has the car ever had the transmission serviced? Check the fluid color by wiping the dipstick on a white paper towel. If its not been serviced in say the last 100K miles, you may want to do a drain/fill. 2 more thoughts - ever notice anything odd with the temperature guage (like creeping up or having the fan come on at odd times). If your engine coolant temp sensor is going wonky it may show up on the gauge. Easy enough to replace (along with the thermostat). Last thing is fuel pressure. It should be around 38-39 PSI. If you have some odd stall outs, it could be a sign that the fuel pump relay is going bad (which in turn is a warning that the fuel pump may be drawing too much current). New fuel pump relays can be had for about $30 and are easy to install.

 

Hey so the PCV system was replaced last year, my husband tried to test the vacuum lines with the cleaner and didn’t seem to have any get sucked in, then he did the glove and it didn’t inflate (which since it was replaced last year we wouldn’t expect it to have an issue), and finally we did the tune up. We replaced the distributor cap, rotor, all new plug wires, and copper plugs properly gapped to .028 and my husband tells me that it is actually idling rougher than before.

Now we replaced the fuel pump about 2 years ago but didn’t replace the fuel pump relay. Do you have a good reference point on how to test a fuel pump relay??

any other suggestions on what we can try next??

thanks for your advice!

 

fuel pump relays are pretty simple devices. there's four wires into the device - two wires actuate the solenoid to close the contact and two wires to pass the voltage current onward. I belive the two large spades are for the current and the two smaller ones are for the solenoid. The typical failure on the FPR is when an old fuel pump starts to draw too much current, the contact starts to get pitted/corroded which builds up heat which in turn weakens the ability of the solenoid to close the contact and that's when the car dies due to no fuel pressure. Wait a few minutes, the relay cools off and it starts to work again! I've never seen a spec but you can probably pull the relay out, put 12V on the small spades and measure the resistance across the large spades. Not sure if you can pop the relay cover off but if you can, you can use some emory cloth to clean up the contact. Easy button is to spend about $40 and drop in a new relay to go with your replacement pump. (its the red one in the relay box up top of the firewall ). Considering your already had to replace the pump, the relay is probably ready to be freshened as well.

PS when your PCV system was serviced, did you do a follow up check for any positive crankcase pressure? If your tech didn't "rod out" the block ports you could still have a blocked PCV system even with new hoses and a new oil separator...

For the idle issues, have you had a smoke test or similar done? You could still have a vacuum leak in an obscure place (like the line that goes back to the evap cannister or a tear in the diaphram of a vacuum actuated device like a fuel pressure regulator, purge valve etc). What you can try doing is blocking off the various vacuum lines to see if that changes anything.

 

yeah my husband did a code scanner and it showed cylinder 3 and 5 misfire. So he did a compression test on it and the other 3 cylinders were reading around 180 PSI and cylinder 3 was reading 30 and 5 was reading 10. He put oil in 3 and 5 cylinder and it did not change the PSI. Any ideas on what could be causing this?? We’ve got an appointment with Volvo but they are so backed up we can’t get in until January 6th at the earliest. We’ve properly maintained the vehicle, we’re the only 2nd owner, and all major maintenance has been done by Volvo including the last Time Belt Replacement.

 

180 PSI is perfect for the NA engines - as for the other two, sigh..... Since the wet compression (with the oil) was the same as the dry, that suggests there's a burnt exhaust valve or two. Other symptoms like brown foam in the oil or oil in the coolant would point to a head gasket issue but this sounds like a valve issue. I'd probably redo the compression test on 3 and 5 to be sure since I'd really expect the engine to run really rough if not at all with two dead cylinders. Another test is to rent an inspection camera (Autozone etc) that gets inserted into the spark plug hole to have a look at valves and piston tops.