Working on a 2001 expedition 5.4, 160k miles. bought it with a misfire. It idles at 400 rpm, and i can only start it with my foot on the gas and slowly let it down to 400 rpm or else it stalls. Figured it was a coil, some are OEM and others are a mixture of aftermarket excitement. just to test I pulled the plugs off the cops one by one to check and see which ones were bad as I have no obd reader and the vehicle isn't registered ( it's a flip car). Seemed that sometimes some would be okay and sometimes the same one wouldn't make any change in idle. Started pulling coils for a visual and 5-8(drivers side) all tubes had coolant over the top of the spark plug. Pulled #4 and it looks dirty but dry as a bone. Cleaned, dried 5-8 and coil boots, replaced spark plugs on that side. This made little to no change. I notice a massive hissing sound behind the throttle body, more so on the driver's side but cannot find any loose or broken hoses. Where should I begin looking next? And could the obviously bad intake gasket (due to the coolant in the tubes)causing it to idle low? From my experience a vacuum leak creates a high idle, but this is the newest vehicle I've worked on, so I don't know

 

Check the elbow on the back of the throttle body coming from the PCV. Also check the lines from the brake booster and evap system.

OBD2 readers start at 20 bucks, you need to buy one.