I just unscrewed my oil cap while the engine was running and noticed there was alot of vacuume going on. Car runs great so the question is....Is that normal? Have yet to experience that in any car ive owned or built. The car di drun rougher whiel unscrewed so Im thinking it was due to the addition of unmetered air being drawn in

Many thanks

Damon

 

Yes, it is normal. And also you are correct in that removing the cap allows too much air to be drawn through the crankcase vent into the intake manifold, so the mixture goes lean. After a couple minutes it will trigger a code.