09 Toyota Corolla 155000 miles. 

Scotty, my 09 Toyota it drive fine with no issue. But not all the time when I press my brakes to come to a complete stop, my engine RPM drops below 500 rpm, like it is about a cut off, but it doesn't.

Sometime when I'm at a light, at idle waiting for it to turns green it drops to 500 rmp at times,  then runs like nothing wrong, but soon as the like turns green it takes off beautifully like nothing happened. I can be in park pressing the brakes nothing's wrong.with it,  1st I thought it might be losing air in the booster, but I checked the valve, that allows air and not out, it is working like it post to, I checked all the hoses see if any air leaks, none.

One day my car did broke down, the alternator went bad, without warning. I put a new one in, and I was thinking maybe that the problem cuz not having enough power can do something like that,  I was told my battery is 3 years old, it was going bad, so I brought the best battery you can get, hoping that's the problem, nope. Still does the same thing.

Later my check engine light finally came on, I forgot the code, but I remember it telling me the evap canister under the gas tank has a problem. But the car drives like there is nothing wrong with it. And a week later after it came on, it went off on his own. Like nothing is wrong with it. Now before I got the car 2 years ago, I've already placed the air filter the spark plugs, and the belt. Using Toyota parts only, to make sure I know when they've been replaced, car runs fine like nothing's wrong with it.

So I decided that I was to clean my airflow mass sensor. Maybe that's the problem, it was dirty, I did use the right spray. Put it back in, the car It idle find like nothing was wrong with, and me pressing on the break, the RPM never drop like it was about to cut off, I'm thinking that fixed the problem, well after driving over 100 miles, the car started doing it again, press the brakes ot come to a stop the RPM drops below 500, likes it's about to cut off.

I decided my next step is to clean the throttle body, to my surprise, there was hardly any dirt on it, and I did use the right spray. I just decided to live with it, I mean the car never cut off except when the alternator went bad. Now my car is making a small pinky noise when I accelerates the gas. 

Every mechanic tells me they see nothing wrong with the car, it's not wasting gas, burning black smoke, but they are not using their scan tool, like you do to see how the engines performing. 

Again when I am driving the car, and when it comes for me to come to a stop, soon as I press the brakes, and you feel all the small g-forces pushing you forward, that's when the engine RPMs go down 500 then later pops back up to normal idling. 

Again sometime you can see the needle move up and down a little bit when I press in the brakes. I live in NC, I wish I could come to you in Tennessee for you to look over my car, I'm stumped, can you please give me  some general ideas what you think is wrong, or what I'm over looking. 

The car starting to get annoying to me. I'm not ready to get another car, I'm sure something small and simple but I don't know what it is. 

Can you please help me. 

Bruce Payne