I have a '95 Mazda 626 DX 2.0 w/auto. It always starts right up, and under power doesn’t skip a beat. But starting it cold, it only runs at about 600-700 rpm (instead of it’s normal high idle). Once it gets warm, it simply will not idle. It is fine at any speed over say 20, but if conditions would normally bring the rpm to idle speed (stopping or slowing to turn), forget it. It’s to the point I have to ride the gas and brake at stop lights and around turns. But even if it stalls, it starts right back up, but I need to ride the gas to keep it running. This is a dangerous situation that I need to fix now! I just replaced the plugs, wires, and distributor cap and I can’t hear any tell-tale vacuum leaks under the hood. Any help would be greatly appreciated as this is my daily driver and about to become a long-distance daily driver!
Clean the throttle body with carb cleaner. If it has an idle air control valve next to the throttle body (likely) clean that as well. Carefully inspect all tubes from the mass airflow sensor to the throttle body, and from the throttle body to the idle air control valve for cracks.
If you don’t find the problem there, you will need a voltmeter and a manual to check the throttle position sensor and the idle air control valve.
You generally cannot hear a vacuum leak. Finding a vacuum leak often involves a flammable liquid from an aerosol can or an unlit propane torch. Be careful.