Audi 99 a4 why only stay on when gas pedal is pressed?

If your 1999 Audi A4 only stays running when the gas pedal is pressed, it could indicate a problem with the idle air control valve (IAC), a vacuum leak, or issues with the fuel system. The IAC helps regulate engine idle speed, and if it's malfunctioning, the engine may stall when not given extra throttle. Additionally, a vacuum leak can disrupt the air-fuel mixture, causing similar symptoms. It's advisable to have the vehicle inspected by a mechanic for accurate diagnosis and repair.