[Mean]

Here is a better way:
GameModeInit:

pawn Код:

SetTimer( "VehicleHealth", 3000, true );

pawn Код:

forward VehicleHealth( );
public VehicleHealth( )
{
    for( new i = 0; i < MAX_PLAYERS; i++ )
    {
        if( IsPlayerConnected( i ) )
        {
            if( IsPlayerInAnyVehicle( i ) )
            {
                new vehicleid = GetPlayerVehicleID( i );
                RepairVehicle( vehicleid );
            }
        }
    }
    return 1;
}

About SetTimerEx, it's crazy because every one will run that timer.

And OnPlayerConnect will be the same, because SetTimer sets a GLOBAL timer, and SetTimerEx sets a timer for only one playerid. Use that code, it's gonna loop through all players and REPAIR the vehicle, not just set the HP to 1000.