98 Contour Vacuum problem??

I've been having problems with my contour since i bought it 4 years ago with 60K on it. I'm having a possible problem with the vacuum, when I'm driving the car will stall when I'm between 25 and 40mph usually when I'm braking. It starts back up immediately after placing it in park. It does tend to do it more when the AC is on. The check engine light has been on nearly this entire time with a AIR/FUEL general code. I've brought it to be checked 3 different times, I've replaced the mass air flow sensor, spark plugs and wires, air filter, and now the timing belt.... The check engine light came back on within minutes of getting the timing belt replaced. The timing belt issue seems to be resolved but i'm still feeling like my engine isnt running at its optimum. And I'm at a loss what to do, as every garage i go to cant seem to figure out my exact issue. PLEASE HELP.

I suspect the brake booster diaphragm has a hole or tear in it or the check valve from the intake vacuum to the brake booster is defective. The brake booster uses vacuum from the engine to apply pressure to the master cylinder on the brakes. If the diaphragm has a hole in it the engine will get too much air upon braking and will stall out. In addition to this there is a one way check valve in the vacuum hose from the engine to the brake booster. To check it disconnect the hose from the engine to the brake booster. Try to blow air into it from both directions.. Air should only flow toward the engine side of the hose. If it flows both ways or neither way replace the hose and check valve.

If the brake booster diaphragm isn't intact or the check valve is defective the symptoms will be a hard pedal on the brakes along with too much air and vacuum leaning the mixture too much to keep the engine running.

I had a similar problem with my 96 Contour were the car's RPM would drop drastically when I took my foot of the gas. It turned out to be the vacuum hose to the inside vent controls. The leak was actually at the transition point from the engine compartment to the cab at the bottom of the firewall and finally connects to the vacuum reservoir just beneath and to the left of the glove box.

I found it by process of elimination after replacing all the vacuum hoses. Follow each of the hoses from the back of the carberator. Start with the one that goes to the bottom of the firewall, disconnect it and plug the connection to the carb. See if that helps. You can also follow the vacuum diagram that is inside the engine compartment to make sure that all connections are tight and hoses are not cracked.

Follow each of the hoses from the back of the carberator.

And this whole time I thought the contour was fuel injected!