For three years now my 2001 Jeep Grand Cherokee Laredo will whistle. Usually when the engine is cold (year-round in Michigan). When the vehicle is idling in the driveway or at stoplights, whenever I take my foot off the accelerator it will whistle too. The only time it won’t whistle is when the gas pedal is being pressed. I’ve had it to a number of different shops to be serviced but once the car is inside or the engine is warmed it will never whistle for the mechanic looking at the vehicle. I’ve been told that it could be related to the IAC motor. What do you think?
I think that while it is whistling you need to pop the hood and try to figure out where the whistle is coming from - at least its general proximity. Using a piece of some kind of hose as a makeshift stethoscope may help.
Check the vacuum hoses. “Whistles” are usually vacuum leaks.
Is is also possible that the intake manifold is slightly loose.