I have a Toyota Celica AT160 and the brake system warning light is off when I start the car, then after a few seconds it comes on.

Car info:

Toyota Celica AT160 1989 Engine 4AGE No ABS

Things I noticed/checked so far:

1. It’s not the parking brake switch I’ve confirmed that.

2. Recently my brakes went poof while on the road. Fortunately I was able to stop. I went to the side and noticed that my brake fluid level was low. Luckily I had some in the back of the car topped it off and build up pressure and was able to make it home.

3. When I got home upon inspection I noticed a small tiny leak on the rear right side of a car. The next day I fixed that, I just cleaned the threads of the flare nut and tighten it snug. Since then i have no leaks.

4. I bled the car and I now have normal breaking pressure and the brakes perform as expected yet the issue still persists. it was a b.itch to bleed, I’ll tell you that.

5. I also noticed that when i pump the brake pedal, the car’s idle RPM goes slightly up. This let me to believe that maybe my master/brake booster is failing.

(The reasoning behind this is, that if the master or brake booster are failing internally whenever I press the pedal, there would be a small vacuum leak in the membrane allowing unmetered air to enter the engine.)

To check, I disconnected the vacuum hose from the brake booster, plugged it and proceeded to press the pedal while the car was running. It did the same thing (revs increased slightly).

When I removed the hose to get a baseline of what the car would behave like if there was a vacuum leak the car revved way higher.

6. The weird thing about this is that whenever I break hard the light turns off, but then comes on after a few seconds.

Additional info

1. I doubt it’s a sensor malfunction because my brakes did fail on me.

2. I also installed new brake hoses 6 months ago.

3. Brake fluids were new and the car’s braking system was properly bled before.

4. I don’t notice The driver’s side carpet be damp, which would indicate that my master is leaking.

I am stumped and out of leads so any input is much appreciated.