960 Rough Idle

[jonnyf90]

Hi All

After a winter of hibernation, my 960 is back on the road after replacing the front control arms and ball joints, a new set of boots on 17" alloys and a mini-service and all is good.

However, it's developed a weird idling problem in the last week.
When idling, the car is shaking slightly, almost as if there's a misfire and looking under the bonnet, the engine is oscillating.

However, under normal driving, it runs perfectly fine and is smooth, although seems slightly down on power.

Anyone have any ideas?
Rooting around previous threads, a vacuum leak might be the culprit, however my OBD-II readout shows vacuum as normal (20 inHg idle, 26inHg off throttle and moving).

When I had the clutch changed last year, my mechanic informed me the flywheel (dual mass!) was slightly scored, but it should be ok. Would this affect the idle so much to cause vibrations?

Cheers

[Laird Scooby]

Add 0.5L of synthetic ATF (i use Carlube ATF-U) to the engine oil, drive it for a few days then do a rest on the fuel ECU. Chances are the hydraulic tappets have become gummed and lazy during the inactivity and the piston rings the same.

The ATF will clean them both restoring compression and valve lift and revive dry oil seals throughout the engine.

[jonnyf90]

Originally Posted by Laird Scooby

Add 0.5L of synthetic ATF (i use Carlube ATF-U) to the engine oil, drive it for a few days then do a rest on the fuel ECU. Chances are the hydraulic tappets have become gummed and lazy during the inactivity and the piston rings the same.

The ATF will clean them both restoring compression and valve lift and revive dry oil seals throughout the engine.

Cheers Laird. I have to run some errands today so I’ll stop at ECP on the way and report back 👍

Cheers

[Clan]

Originally Posted by jonnyf90

Hi All

After a winter of hibernation, my 960 is back on the road after replacing the front control arms and ball joints, a new set of boots on 17" alloys and a mini-service and all is good.

However, it's developed a weird idling problem in the last week.
When idling, the car is shaking slightly, almost as if there's a misfire and looking under the bonnet, the engine is oscillating.

However, under normal driving, it runs perfectly fine and is smooth, although seems slightly down on power.

Anyone have any ideas?
Rooting around previous threads, a vacuum leak might be the culprit, however my OBD-II readout shows vacuum as normal (20 inHg idle, 26inHg off throttle and moving).

When I had the clutch changed last year, my mechanic informed me the flywheel (dual mass!) was slightly scored, but it should be ok. Would this affect the idle so much to cause vibrations?

Cheers

The Inlet manifold gasket breaks up after a while and sucks in air on one cylinder ... spray some brake cleaner around the joint with the head on each of the 6 branches when idling see if it affects the running .

Coils can go faulty as well causing a similar symptom ...

[mjk164]

As Dave above says, it might just be that the hydraulic lifters are a bit sticky in which case what he recommends should help resolve the issue. On my 960 that I used for many years, I only ever used fully synthetic oil and, being thinner, resolved all my issues with valve lifter wear and being sticky when cold. More importantly, I would also take off the valve cover and carefully check all the connections from the wires that come from the two amplifiers (one on each side, down low, of the inlet manifold) and go to each spark plug ignition coil. These coils get warm in use and, over time, hardens the insulation close to the attachment clip on the top of the coil. It only hardens for about an inch or two but, with repeated coil removal for plug maintenance, this insulation peels or breaks off and the exposed copper wires, harden and begin to break. When I had ignition problems, I found I had to renew the wires to all 6 units, not the whole length back to the amplifiers, but for a few inches from the coil. After I had done that, all my ignition issues had gone and the engine never ran so well. So, I would check.

[jonnyf90]

Thanks for suggestions Clan/mjk.

Wouldn't coil issues also affect normal driving as well though?

Cheers

[Laird Scooby]

Originally Posted by jonnyf90

Thanks for suggestions Clan/mjk.

Wouldn't coil issues also affect normal driving as well though?

Cheers

They probably would but usually more at the lower end of the rev range and possibly the very highest end. In the middle the coils output will be at its highest due to resonant frequency of the coils themselves. This usually overcomes any mixture deficiencies of a weak crusing mix and keeps it firing.

However, if what i suspect is correct about the lifters etc from the hibernation then you should notice a difference after af ew days with the ATF in the engine. Then you will have a much better idea of what the engine is or isn't doing, often things like this are a simple fix so try that first, if nothing else it levels the playing field so there aren't compound faults (many with minor symptoms creating one bigger symptom not necessarily related to the minor ones) throwing out red herrings.

[mjk164]

In my experience, not necessarily. It may show up as an occasional slight misfire but more noticeable when at tick over. It only takes a few screws to check.

[StanC]

Originally Posted by mjk164

As Dave above says, it might just be that the hydraulic lifters are a bit sticky in which case what he recommends should help resolve the issue. On my 960 that I used for many years, I only ever used fully synthetic oil and, being thinner, resolved all my issues with valve lifter wear and being sticky when cold. More importantly, I would also take off the valve cover and carefully check all the connections from the wires that come from the two amplifiers (one on each side, down low, of the inlet manifold) and go to each spark plug ignition coil. These coils get warm in use and, over time, hardens the insulation close to the attachment clip on the top of the coil. It only hardens for about an inch or two but, with repeated coil removal for plug maintenance, this insulation peels or breaks off and the exposed copper wires, harden and begin to break. When I had ignition problems, I found I had to renew the wires to all 6 units, not the whole length back to the amplifiers, but for a few inches from the coil. After I had done that, all my ignition issues had gone and the engine never ran so well. So, I would check.

MJK - what wire did you use to replace the old, hardened, wire and where did you obtain it? I'm asking purely because I'm concerned about the ignition wiring loom on my 960 - whilst it is currently ok (touch wood), it can only be a matter of time before it starts giving trouble.
Incidentally, like you I've only ever used fully synthetic (Mobil 0w-40) engine oil in my car, changed annually or every 5000 miles, and at 179000 miles I've never had hydraulic lifter issues.

Thanks,
Stan.

[mjk164]

Hi Stan, I don't have my 960 now but it was 1993 2.9 and had 380k on the clock. The wire I use for nearly all regular car wiring is standard 8 amp single wire from Halfords (HEF721), available at least in red and black. On the coil units I soldered the new wire to the Lucar clips; with care you can use the original ones as they are Lucas and not the rubbish that comes from other countries. As I said earlier, you only need to replace an inch or 2 back from the clip which sees the heat and hardens the insulation. The quality of wires used in these Volvos is good and, if not in a "working" area i.e. wires that have to be handled regularly for maintenance like for spark plug access, if left undisturbed, will last for years. I connected the new short length of wires to the original with simple torpedo butt connectors and crimp pliers. There is sufficient black plastic harness covering to pull back over the repaired wires. I always take the opportunity to visually check the wires in and around the engine to ensure the securing clips are good and there are not touching "wear" areas. After sorting out these coil connections, that resolved all sorts of odd running issues. Good luck.