No, not even a little. However, your fresh air intake is stunted a bit. The cover you're talking about covers the grill in front of the windshield, and only limits the air intake into the vehicle itself. It is independant of the engine compartment. There are holes that drain the cowl behind the fenders. These holes are the only place where you will be able to get fresh air for your heater.
EVERYONE BEAT ME TO IT, DAMN!<P ID="edit"><FONT SIZE=-1>Edited by thespazardman on 04/18/01 05:47 PM (server time).</FONT></P>
Not the engine but it does affect the defroster. It's a catch 22 as I tend to need the defroster working properly when it's raining which would imply taking off the cowl cover, which should be installed when it's raining.