2f will not idle at times. So jumped in the cruiser for a trip up the street. Would not idle. Thought maybe a vacuum leak. Would not even get 500 rpm at idle. Cut engine off and got my wife's mirror. Upon inspection from underneath I don't see a crack in the manifold. Started the truck back up and idled like a kitten. This is not a cold engine symptom as it does it well after warm up. I had the HG done earlier this year. Pulls fine when on the gas as well. Other concern is i found oil on the outside puddled under a spark plug. I did recently add a couple quarts of oil but doubt I spilled enough to get back there. Any thoughts?