Well, we have seen this post a number of times, but here goes. I have been battleing rough idle on my 93 850 for about a year now. No fault codes, and no failures, but a pronounced rough idle. I have folowed this board and have applied my mechanical knowledge as best I can. Machinist for 19 plus years now.
I have tried Cap rotor plugs and wires. Fresh fuel filter. Motorvac cleaning at Indie shop that I have been a customer at for 20 Plus years. New O2 sensor. cleaning Throttle body, no EGR air pump on 93. Checked vacuum lines. Purchased RPM sensor, not installed yet. Removed Cam sensor, visual check cleaned RPM and Cam sensor conection. Replaced Fuel pump relays. Checked fuel pressure at idle and received 40 PSI reading.
Only thing left in my mind is to replace the fuel pump. Rough idle seems more pronounced when tank is down to 6-7 gallons of fuel. I am debating buying the whole pump assembly, or just the replacement cartridge. Any thoughts on this on would be greatly appreciated. Only other thing I could think of would be a faulty injector, but I do not know a good way to inspect those as a DIY project.
Original owner, 84000 miles. 6th volvo owned