Poor idle
 

My 86 911 has a strange idle -

When it is warm the idle has a rhythmic lope - if I put it in gear and slightly engage the clutch the idle will stabilize and stay that way until the engine is revved again - then it will go back to the lope.

I have replaced the ISC valve with no change.

Do you suppose I have a throttle plate that needs to be closed down a hair (is this even possible) or perhaps an air leak?

Thanks!

Great forum.