F-150 Shakes When Braking, Only When A/C Is On

I have a 1997 F-150 4.6 Liter 2WD AT
It rides and brakes smoothly when not running the A/C
When I switch on the A/C it still rides and runs smoothly and still brakes smoothly at first.
After a few minutes, when I brake, the front end shakes slightly. While not braking it’s still fine.
The problem doesn’t go away immediately when I switch of the A/C, but does eventually.
However, on rare occasion the front end will start shaking like I have a square tire, even when not braking.
This never occurs when I’m not running the A/C
Pads and rotors seem fine, tires are good, on visual inspection.
A/C blows cold and the clutch seems to engage/disengage properly
Any suggestions?

The next time this happens with the engine idling, open the hood and with the handle of a scewdriver rap on the idle Air Control valve. If the engine idle speed changes replace the IAC valve.


Thanks for the input, I’ll give that a shot

Tester, It very rarely does the constant shake, but I tried what you said after running the A/C
to get the “Brake Shake”, there was no change in idle speed.
Do you think it needs to be in the constant shake mode for this test?

Any other ideas?