I have a 97 Ford F150 with a 4.2L engine. When the air temp is around
35 or below I get a very loud whistling coming from the engine. It occurs mainly between 1500 to 2000 rpm but varies with engine load and throttle position. It is so LOUD I can't tell exactly where it's coming from. Could it be a vacuum leak or bad air pump maybe? Any suggestions will be greatly appreciated as I am about to start wearing ear plugs. Thanks, jeff