At 04:29 PM 3/11/2011, A PETER MARSH wrote:
>Any suggestions where to look for a reason for this?

Test your closed-throttle switch operation and report.  Bentley
24.59, left column*

*Worn throttle bodies may require some compromises, but bottom line
is that with the engine idling and throttle allowed to close slowly,
the switch has to close reliably.

If that's good check the basic idle speed with idle speed valve
unplugged - it will cause symptoms sounding like (in the absence of
numbers...) your description if it's set too high.

Yrs,
d