Sounds weird that it only does it at idle (Bavarian). Sort of rules out plugs/ignition etc..., but I'd try plugs anyway

Use some areostart and go around all joins if you have an airflow meter from the meter back and as much around throttlebody and manifold conennections as you can reach. You'd be amazed how many cars have leaks. If you have one the engine revs will rise slightly. Miss will be caused by motor drawing in unmetered air and running slighly lean.

You'd be amazed how common this is.

It may be a long shot, but if you dont have much else left to try it's an easy test.


Cheers Matt