2002 f150 fx4 5.4 166k miles

idle goes up and down when heat is turned to setting “panel/floor”. If heat is on and just in “panel”setting it stays consistent. I removed plastic cover from top of engine and inspected all vacuum hoses. Everything looks good. When the idle jumps I do hear a sucking noise from what seems to be passenger side of engine but not 100% sure. It may just be normal intake noise🤷‍♂️. I used propane to try to find vacuum leak with no luck.

heater core replaced 30k ago. Maf cleaned 5k ago. Pcv, hose, and elbow replaced 500 miles ago. No stored codes. Any suggestions?

 

Pretty sure panel/floor engages the A/C compressor, so I'd look into that.

 

Yeah, as COS said, go watch your A/C compressor and see if the idle is fluctuating with the clutch engaging.

 

ok, yes ac compressor engages and starts spinning as idle goes up then stops when returned to normal idle. Should I look for leaks in the ac system? Air temp outside is below 35 right now as well. I assume the pcm is adding fuel to accommodate for what though?

 

Not necessarily. If you suspect it's low on R134A or PAG oil, you can always unplug the low pressure switch and it won't turn on at all.

 

is it normal for idle to fluctuate with the ac compressor every 30sec or so? I’ve never noticed it but as this trucks gotten older I’ve paid attention more to everything that seems irregular.

 

It is probably low on 134A if it is cycling that much.

 

cool, I will check it out. Thanks for the info