Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
Most unmodified engines will have very little valve overlap at idle.
A small block v8 with a performance camshaft will lope at idle, a stock four cylinder Honda engine should not.
I have a amateur question, how do you tell the difference between looping because of valve overlap and a misfire at idle?
A scanner may show significant shifts in fuel trims due to misfire.
If available a cylinder contribution test is a great tool either with a scanner or an oscilloscope.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
As far as road-going passenger vehicles, noticeable idle loping is almost always a problem. :silly: Even on vehicles with aggressive VVT systems that make use of scavenging and catalyst heating strategies, your average car owner won't know the difference.
