lever mounted near the vehicle steering wheel can send a signal 84 which can be used to close the valve 34 when braking is desired during the regeneration mode the control should modulate the back pressure valve 34 so that an essentially constant trap inlet temperature is maintained this temperature should be approximately 1100 u00b0 f to 1200 u00b0 f for uncatalyzed traps and 750 u00b0 f to 850 u00b0 f for catalyzed traps the most direct means for controlling exhaust temperature is to sense the exhaust temperature at 70 and to close the back pressure valve 34 incrimentally whenever the exhaust temperature is lower than the desired temperature and to open the valve whenever the temperature exceeds the desired temperature use of temperature as the controlling parameter requires careful dynamic matching of all system components to prevent valve overtravel and the attendent overshooting of the exhuast gas temperature which could damage the particlate trap and adversely effect engine emission and performance care must also be taken to prevent exhaust gas over temperature during regeneration and following a sudden increase in fuel flow the back pressure valve must open quickly when the engine fuel input is suddenly increased the back pressure valve must open very quickly because the fuel input can increase from nearly zero input to maximum input within two revolutions of the engine this quick response requires some means of anticipating the change in fuel input and or a means of slowing the rate of increase in fuel hence a rack position sensor 78 may be.