Volvo 940, B230FK -1995 rough idle...

Normally, I think I can fix almost everything on a car, but this one... Ok ,
please read and be surprised (ehrm... ok, I know...)...

I've tried everything...
Ignition:
Spark plugs - new
Cables - new
Distributor cap - new
Distributor parts, all new..

Fuel:
Injectors cleaned
Wireing checked...
Fuel pump, ok
Fuel press., ok
Lambda, ok

Air:
New filter
Hoses, ok
AMM, ok
Intercooler, ok
Turbo, ok

Else:
Normal temp.
Oil consumption, ok - close to nothing.
No bad noises...
Enough power while coasting and accelleration...
Fuel consumption, ok (according to user manual)

Once in a while the engine seems to stall, but catches up and runs ok
again...
No system in the "caughs". Very random.
Warm engine and idle at factory settings.
It's like a human flu... random caughs...
A very mild smell of burned oil... Strange...
Example: Red light at a crossing, and stopping, engine at idle, rough idle
and a mild smell of burned oil...

Help!...
Anyone...

 

Hmmm. I have the same problem. Here's another vote to find the solution.

Once before though it was faulty plug cables... but you say you've replaced
those.

TKM

 

With the limited information you have provided I'd suggest that your
symptoms are consistent with a lean stumble. Over a period of time
intake valves will develop carbon deposits on the surface constantly
exposed to incoming fuel. At some point the deposits become heavy
enough to absorb fuel as it is injected leading to a shortage of fuel
in the cylinder. This is especially true at closed loop/hot idle and
is much less obvious under throttle.

We use a Snap-On/Motorvac fuel system cleaner to address this
condition. Your mechanic can provide more information.

Regards

 

Thanks for trying to help.
I'm sure someone in this community knows the problem and the solution.

Well known problem the carbon deposits.
But a few weeks ago I had to mount a new cylinder head gasket because of a
crack in the gasket causing a coolant leak.
An inspection of the cylinder head revealed nothing strange.
No deposits on the valves or in the combustion chamber.
Cylinder no 4 had traces of oil on the pistion top. Not much, but using a
paper towel I got small traces of oil. The other cylinders was all fine.
The oil consumption is normal. Close to nothing.

The car runs well, and has enough power.
The problem started more than a year ago, so I'm starting getting a bit
xxxxx (fill in with suitable word...) now.

Ask the Volvo shop... no chance... They won't answer unless they get paid
for it...
Once I tried, but the answer was: spark plugs, cables, water in the fuel,
and so on...
Nothing revolusionary new...

 

I had this exact problem and now is cured. There seems to be an issue with
the engine management system. Here in the UK, an item on the BBC consumer
advice program called "Watchdog" revealed that quite a few Volvo owners were
having problems like this. Volvo agreed to modify the EMU free of charge to
owners of certain types of Volvo. Mine was one of these so I had it done
and now it's great. No idle problems. Here is the TV program website link
http://www.bbc.co.uk/consumer/tv_and_radio/watchdog/reports/transport/transport_20061205.shtml
hope this helps.
Steve

 

After trying many of the solutions on the forum with no success (thanks just the same), I fixed my problem which was an intermittent rough idle. The problem started when I tightened a loose exhaust pipe flange at the exhaust manifold. It turns out the transmission to front exhaust pipe mount had snapped allowing for a cycling rough idle. I repaired it and the vibration disappeared.