How to make an RC car move forward using a microcntroller

I can control my rc car steering wheel left, center and right. But I can not make it move forward.

Im using the LPC2148 microcontroller.

Any help will be great!!!

================

this is my code:

=============

#include "pwm.h"

void pwm_init()
{
    PINSEL0 &= ~(3<<14);
    PINSEL0 |= (1<<15);        // select P0.7 for PWM2

    PINSEL1 &= ~(3<<10);
    PINSEL1 |= (1<<10);        // select P0.21 for PWM5


// new
    PWMTCR = 0x02;            // reset PWM
    PWMMR0 = 0x00124F80;    //set pwm period (20mS)
    PWMPR = 0;                // prescaler disabled
    PWMPCR = 0x2400;          // enable PWM2&5 output and chosen for single edge PWM
    PWMTCR = 00001001;      // counter and PWM enabled
    PWMMR2 = 0x00;  //0124F8;      // set Match 2 to 0 ticks
    //PWMMR5 = 0x00124F7F;    // set Match 5 to 0 ticks
    PWMMR5 = 0x00049F0;

    PWMMCR = 0x0000003;          // reset on Match 0
}
void left()
{
    PWMMR2 = 0x00019A28;
    PWMLER = 0x04;
}
void right()
{
    rprintf("hola\n");
    PWMMR2 = 0x000024F8;
    PWMLER = 0x04;
}
void straight()
{
    PWMMR2 = 0x000124F8;
    PWMLER = 0x04;
}
void go()
{
    PWMMR5 = 0x0001D4C0;
    PWMLER = 0x20;

}
void stop()
{
    PWMMR5 = 0x0000EA60;
    PWMLER = 0x20;
}
void throttle()
{
    PWMMR5 = 0x000F4240;
    PWMLER = 0x20;
}
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thanks =)