Idle dropping when engaging to R or D, while foot is on the brake pedal and the a/c is turned on

1. Vacuum leak: A vacuum leak can cause the idle to drop, making it feel like you are pressing the brake pedal when you shift to 4x4.
2. Throttle position sensor (TPS): The TPS is responsible for sending a signal to the engine management system regarding the position of the throttle. If the TPS is malfunctioning, it can cause the idle to drop and result in a similar feeling as if you were pressing the brake pedal.
3. Transmission: A problem with the transmission can cause the vehicle to feel like it's slipping or dragging, making it feel like your foot is on the brake pedal.
4. Transfer case: If there is an issue with the transfer case, such as low fluid levels or a problem with the shift mechanism, it could result in a similar feeling as if you were pressing the brake pedal when shifting to 4x4.

have the fault codes read to find the sensor that has failed
if it happening when you have the foot on the brake, it could be a problem brake booster

Leaver down some how and pull release.

Is your ABS working properly? Under heavy braking the ABS should engage and 'pulse' the brakes on/off. It is normal to feel the brake petal flutter or pulse under your foot.

Under light braking there should be no pulsing as the ABS does not engage and you have changed the rotors and pads.

almost sounds like the cruise control is engaging

oil the ratchet section of the pedal

The booster uses vacumn to assist your foot pressure. A leaky seal or diaphragm in the booster or a bad hose from the engine to the booster will cause the pedal to drop as it loses power assist. I think the brake light switch is mounted under the dash by the brake pedal. Fix the booster now, it may save your life.

When was the last time you changed the front brake pads?
Try this:
Keep the brake pedal pressed down and start the car, after it idles for about 10 second let go of the pedal. If the light comes on just as you leave the pedal - try pumping it a few times, turn the car off and pump the pedal some more until it becomes real hard.
Then, keeping your foot to the pedal, start the car.
Idle for about 10 seconds, let go of the pedal and press it again rel fast.
If the light doesnt come on again - it means you have a leak of some sort or that the main brake pump should be replaced.

Good luck.

Sounds like the cable is stuck also check the catch on the foot pedel

Hi,
From your description this appears to be a Brake servo issue.
The brakes are assisted by a vacuum created from the draw off the inlet manifold, it gives assistance too the brake pedal pressure by a large tank/cylinder mounted on the Bulkhead/firewall.
I feel that the sound you a hearing is air being draw into the Brake Servo from the foot pedal seal and the reason for fluctuation in the engine is the vacuum from the inlet manifold is being upset.
Attention I suspect should be addressed to the Brake servo/pedal seal or gaitor.
I hope this clarifies your thoughts?
Please remember to rate my effort.
Paul 'W'
Onyer~EDSon(:0) {#><U.K.