volvo 240 engine running problem

i run a 1989 240 volvo estate dl 2.3, using a b230k engine, with a problem.namely the engine will not run correctly despite a lot of time and effort.
The ignition system is a fully electronic bendix unit with no distributor electronics, it merely being an ht distributor.
The engines power changes in a very unpredictable way.
The vacuum reading at idle is 21inches and stable.Originally the car had a solex downdraught carb that I replaced with an su kit from burlen fuels using the bdk needle.I have had the head off and checked for sticking valves pick up on the stems etc but all is ok.
The engine originally had egr and a pulsair system system removed before i got the car.
More often than not the engine as a very lumpy idle,with co readings varying by say 1% or more,could the pulsair system being removed have upset the running.
I was carefull to check the inlet manifold for cleanliness,using carb cleaner to check for air leaks revealed nothing plus the ignition system checks out using an analyzer any ideas

[Peter Milnes]

Another candidate for inlet tract cleaning and ignition power module (feeds the coil from the Ignition Control Unit) earthing and heatsinking. Inlet tract cleaning also involves cleaning of the Idle Air Control Module where fitted. You may also be suffering from an air leak where the carburettor joins the inlet manifold. Spray the join with WD40 whilst engine is running at idle. If tickover smooths out then you have a leak at that point. To remedy this replace the carburettor gasket.

All the best, Peter