| i think you may need a product called an oil catch can, gtt sell one over here, oil inside my intercooler july 05, only a fine coating but noticable al the same
i suggest if you had an air leak/loss of pressure in the system you would notice it all the time
for example if intercooler not fitted correctly air leaks an cause massive surging in engine idle speed
you may need to look further more to sort your idle | 
