The air temp sensor is not critical to operation. It supplements and refines other signals and inputs to the ECU. Therefore, you may have an electrical problem associated with this sensor. Try using an ohm meter and take a reading, with the engine cold, of the air sensor directly at the sensor and then at the ECU connector. The readings should be nearly identical unless there is excess resistance in the wires leading from the sensor to the ECU connector. If the resistance is much higher from the ECU end, suspect a b5d ground at the bundle of wires screwed to the manifold or badly frayed wires. Then take out the sensor, drop it in pretty warm water for a minute or so( just the sensor part not the electrical connection) and repeat the measurements from both ends. The resistance should be much lower.......but the same at both ends. If I remember correctly, the reading should be about 500 ohms cold and perhaps 150-200 ohms warm. Not absolutely certain of these numbers.

As far as a vacuum leak goes, try using a long piece of plastic tubing. Run the car, put one end in your ear and move the other end around everywhere there are gaskets including the injectors, injector holders, manifold gasket, all the hoses and their connectors and the one way valve on the hose between the manifold and the brake booster. If there is a leak, you should hear a sucking or whistling sound. Good luck