Peter. I had this on a car I worked on before and it baffled me for a while. I believe I finally tracked it down to either a faulty air flow meter sensor, or the wiring a plug that goes to it. Fiddle around with the plug and wiring that goes to the meter while the engine is running. Move it around and see if you can hear a difference to the way the engine is running.
col
December 2010
Peter. Have you tried cleaning the idle vavle controller?
col
December 2010
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