I have a 99 F-150 4x4 with the 5.4... While idling it will stay around the 800 rpm range for awhile then what sounds like a switch clicks and it goes up to 1100 rpm then repeats thee cycle... It does this cycle constantly, hot or cold, and I'm just curious as to what makes it do this?

Thanks,
Willie

 

Do you hear this click with the ac on? if so its the ac clutch engaging and disengaging the pcm will increase rpm to handle load, if it is cycling too much 6-8 times a minute indicates low refrigerant pressure levels, get charged or low pressure switch malfunctioning IMO

 

That's exactly what it sounds like, but the ac is off...

 

Ac cycling switch? its on top of the dryer, passenger firewall behind engine harness connector brackets

 

Would that be the AC clutch switch? More Information for MOTORCRAFT YH1462 I haven't had a chance to look for the one you described I'll try and get to that tomorrow... Thanks again!

 

And also, if I disconnect the switch will I see a difference in the idle at all?

 

IF you disconnect the connector at the pump or the dryer it shouldnt engage, no a/c, i would think, i never tried