volvo 240 rough running

If this car has K-Jet (still amazes me they used that old system so long over there) then the first thing I'd do is check very carefully for vacuum leaks.

I'm pretty sure that it will be K-Jet; I think it was a couple of years later that we finally moved on. It may have been old, but it was extremely reliable and durable. I'm surprised that carb. models were still available alongside K-Jet.

Certainly check for air leaks, including the injector seals (squirt a little water over the injector seats while the engine is running - if it gets drawn in, the engine will falter or stall) and the pipes that go to the auxiliary air valve (sits on the side of the valve cover on the top of the engine), and make sure that the fat rubber boot under the inlet manifold is still properly in place between the throttle body and the air flow meter. Also squirt a little water around the inlet manifold gasket.

But I would start with checking the ignition componets, particularly the distributor cap and rotor arm. If you have access to a timing light or spark tester, make sure you are getting a healthy spark to all four cylinders.

When you say it sounds really noisy, where from? What sort of noise?

Does the problem change as the engine warms up?

(which I will investigate tomorrow)

I had a friend round today, and tried starting it up again. There was definately unburnt fuel vapour being blown out of the exhaust. The contacts inside the distributor cap were green (copper oxidation?), so cleaned them off, cleaned the HT leads, and checked for corrosion at the spark plug and distributor ends. It ran ok when restarted, but reverted back to it's misfiring at 500rpm after about 30 seconds.

Pretty sure it's an electrical problem now, when it is light again outside, I'll check again further.

The engine. It was consistent with misfiring.

When I had the problem the other day, it carried on until I was able to get the car home, and the engine was up to temperature.

Thanks all for the advice so far!

-Douglas