1990 m have Mazda runs and when u stick it in drive it dies unless u hold brakes and give it gas or in reeve's it works fine and will sit and idle I have changed the brake booster cause u all said vacuum leak so I did that what else should I do?
You probably have a bad Idle air Control Valve, IACV. It is located on the intake manifold nest to the throtle body. It is either vacuum or lectrical solenoid that pushes pluger to let air around the throttle body through ports to keep idle steady when engine load changes. Sometimes the cooalnt runs lines through them too act in a cold starting situation and react to changes in temperature. Sometimes you can clean them if they still work. Remove it and if you can get the pluner to move when you revmotor, with IACV removed but connected to vacuum or elctrical connector and coolant lines, and see if pluger reacts. Then you can clean it and clean out the ports too. Always spray from outside in towars the intake tract as deposits develop nearest to the intake tract side or end of port as air travels that way and spraying cleaner the opposite way can make clogs worde. If plunger does not react it needs to be replaced. If it isnot that you may have to check the fuel pressure to make sure your getting enoguh gas and check the pressure regulator by removing vauum line, if it changes pressure, goes up, then it is okay.