Hi All,
I have a 97 XLT with 4.0 SOHC. I have a problem when I move the heater into the defrost (upper vent) position. At idle, when in this position I hear a loud click and the engine bogs down to about 400 rpm then recovers. Three seconds later the cycle repeats. When the heat selecter is in the floor/defrost position the problem still exists, but it doesn't seem to bog down so badly.
Any suggestions on what might be causing this? FWIW, I do have the infamous blend door problem.
Thanks for any input you can offer.