If you're stopped at a traffic light with you foot on the brake pedal, slowly goes to the floor, and releasing the pedal and pressing it down again results in the same thing, then you have an external leak, or a bad master cylinder.

Check the fluid level in the brake master cylinder. If the master cylinder is full of brake fluid, and there are no external leaks, then the master cylinder must be replaced.

By external leaks I mean leaks at brake hoses, brake wheel-cylinders, and so on. You can inspect for these yourself, or you can have a mechanic do it. The important thing to remember is that if brake fluid isn't leaking out of the brake system anywhere, the master cylinder must be replaced.

COLD ENGINE STALLS -- If your car has an automatic transmission, and the cold engine stalls when you put the transmission in gear, the problem may be caused by an improperly adjusted choke kick-off.

The choke kick-off is a device on a carburetor that opens the choke plate slightly when a cold engine is started. Sometimes the choke plate doesn't open as it should, and stalling can result.

One way to check the choke kick-off is to remove the top of the air cleaner and watch the choke plate while someone else starts the engine. It should open slightly when the engine is started. If it doesn't, the choke kick-off must be adjusted. Or if the choke plate is inoperative (the choke kick-off linkage doesn't move at all when the cold engine is started), the choke kick-off must be must be replaced.

If the choke is working, another likely cause is a fast-idle speed that is set too low. The fast-idle cam should be positioned as instructed in the shop manual for your car, and then the engine rpm should be checked with a tachometer. If the rpm isn't at the car maker's recommended specification, it must be adjusted to meet it.

Some carburetors have two kick-offs, by the way -- one opens the choke plate a little bit at startup, and the other opens it a little bit more shortly thereafter. Now if checking the choke kick-off, or checking and adjusting fast-idle speed sounds harder than you can handle, have a mechanic check it.

USING GASOHOL. Gasohol is sold at many services stations around the country. It's a mixture of nine parts gasoline and one part ethanol (a type of alcohol).

In older cars, the ethanol tends to loosen foreign particles in the fuel tank, sometimes clogging the fuel filter. So if you start using gasohol regularly, and your engine suddenly begins to perform poorly, chances are it's a clogged fuel filter. Replacing the filter usually takes care of it.

Remember, a car has two fuel filters -- one between the fuel pump and the carburetor, and a filter-sack in the bottom of the gas tank. In most cases, replacing the filter between the fuel pump and the carb solves the problem. However, insevere cases, it may be necessary to remove the gas tank and service it.