before any embodiments of the invention are explained in detail , it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings . the invention is capable of other embodiments and of being practiced or of being carried out in various ways . also , it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting . the use of “ including ,” “ comprising ,” or “ having ” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items . unless specified or limited otherwise , the terms “ mounted ,” “ connected ,” “ supported ,” and “ coupled ” and variations thereof are used broadly and encompass direct and indirect mountings , connections , supports , and couplings . further , “ connected ” and “ coupled ” are not restricted to physical or mechanical connections or couplings . fig1 illustrates one possible pressure washer 10 that employs the invention . as one of ordinary skill will realize , the invention described herein is suitable for use with most pressure washers that output a pressurized liquid . as such , the invention should not be limited only to pressure washers 10 similar to the one illustrated in fig1 . the pressure washer 10 is a mobile pressure washer that includes a trigger - actuated gun 15 , an internal combustion engine 20 , and a pump 25 . the engine 20 drives the pump 25 , which draws fluid , typically water , from a source ( e . g ., an onboard reservoir , a garden hose , an external tank , etc .) and selectively delivers the fluid to the gun 15 , via a hose 30 , under pressure . the gun 15 includes a trigger assembly 35 that allows the user to selectively discharge a flow of water from the gun 15 . typically , the user squeezes the trigger 35 to open a valve ( not shown ) and begin the discharge of high - pressure fluid . when the user disengages the trigger 35 , the valve closes , and high - pressure flow is inhibited from exiting the gun 15 . fig2 illustrates a pressure washer 10 a that includes the engine 20 supported by a frame 40 having wheels 45 to allow for movement . in the illustrated construction , a one - cylinder horizontal shaft internal combustion engine is employed . of course , other arrangements may employ a vertical shaft engine and / or a multi - cylinder engine if desired . in addition , other engine types ( e . g ., diesel , rotary , etc .) could also be employed . with reference to fig3 , the engine 20 includes a throttle 50 that is movable between an idle position and a wide open position to vary the flow of fuel and air to the engine 20 . when the throttle 50 is in the idle position the engine 20 operates at an idle speed , and when the throttle 50 is in the wide open position the engine 20 operates at a desired engine speed . the engine 20 also includes a crankcase 55 , a piston ( not shown ), a crankshaft ( not shown ), and one or more cam shafts ( not shown ). the crankshaft rotates in response to reciprocation of the piston to produce usable shaft power . the cam shaft or shafts are coupled to the crankshaft such that they rotate at one - half the crankshaft speed to actuate intake and exhaust valves for the engine 20 , as is well known in the art . a governor 60 is coupled to the throttle 50 to control the throttle position to maintain the engine 20 at the desired engine speed during operation . the governor 60 includes a speed sensor ( not shown ) that senses the actual operating speed of the engine 20 . if a typical mechanical governor is used , flyweights rotate in response to the rotation of the engine crankshaft or cam shaft such that the flyweights rotate at the engine speed , or one - half the engine speed ( the cam shaft speed ). in the illustrated construction , the speed sensor engages a governor shaft 65 that extends out of the crankcase 55 and engages a governor arm 70 . the governor arm 70 moves through an arc in response to changes in speed of the engine 20 . a link arm 75 includes a first end 80 that connects to the governor arm 70 and a second end 85 that is coupled to the throttle 50 . thus , movement of the governor arm 70 produces a corresponding movement of the throttle 50 . a governor spring 90 is connected to the engine 20 and to the governor arm 70 to bias the arm 70 toward a first or wide open throttle direction . the governor arm 70 includes an extension 95 that defines a plurality of apertures 100 . a second spring 105 includes a first end 110 that is coupled to the extension 95 using one of the apertures 100 , and a second end 115 coupled to an idle control lever 120 . the spring 105 can be connected to any one of the apertures 100 to adjust the effect of the spring 105 . the idle control lever 120 is pivotally coupled to the engine 20 such that it rotates substantially freely about an axis . an idle lever 125 is coupled to the idle control lever 120 and an idle down controller 130 . with reference to fig7 , 8 , and 10 , the idle down controller 130 includes a housing 135 , a spring 140 , and an actuator 145 positioned within the housing 135 . in the illustrated construction , a one - piece housing 135 is employed , with other constructions employing multi - piece housings . the housing 135 includes a threaded aperture 150 ( shown in fig8 ) that provides for fluid communication to a sensor aperture 155 . the sensor aperture 155 allows for the communication of the fluid pressure from the threaded aperture 150 to the actuator 145 . the sensor aperture 155 is about one - quarter of an inch in diameter , with larger or smaller apertures 155 also being suitable . the relatively large size of the aperture 155 reduces the likelihood of clogging in the controller 130 . the housing 135 also includes a shoulder portion 160 and a groove 165 that cooperate to attach the idle down controller 130 to the engine 20 , as will be described in more detail with regard to fig5 . the actuator 145 is movably supported by the housing 135 such that it can move between an idle position ( shown in fig7 and 8 ) and a normal speed position . when the actuator 145 is in the idle position , it overrides the governor 60 and forces the throttle 50 toward the idle position . when the actuator 145 is in the normal speed position , the idle down controller 130 allows the governor 60 to control the speed of the engine 20 . the actuator 145 includes a piston portion 170 and a connecting portion 175 that extends outside of the housing 135 . the connecting portion 175 engages the idle lever 125 to connect the actuator 145 to the throttle 50 . the piston portion 170 is in fluid communication with the sensor aperture 155 to allow the fluid pressure to act on the piston 170 . the spring 140 is positioned within the housing 135 to bias the actuator 145 into the normal speed position ( illustrated in fig7 and 8 ). fig5 illustrates the attachment of the idle down controller 130 to the engine 20 . the engine 20 includes a support bracket 180 that defines an aperture sized to receive a portion of the housing 135 . the shoulder portion 160 engages one side of the bracket 180 such that the groove 165 extends through the aperture . an e - ring 185 engages the groove 165 to lock the idle down controller 130 in its operating position . also visible in fig5 is a small breather aperture 190 formed in the end of the housing 135 opposite the actuator 145 . the breather aperture 190 provides an air flow path into and out of the housing 135 to allow the actuator 145 to move freely . as shown in fig4 , the pump 25 is coupled to the engine 20 such that rotation of the engine 20 produces a corresponding rotation of the pump 25 . in some constructions , a gearbox or other speed changing device is positioned between the engine 20 and the pump 25 , with preferred constructions employing a direct connection such that the pump 25 rotates at the same speed as the engine 20 . in the illustrated arrangement , a triplex pump is employed with other types of pumps 25 also being suitable for use . the pump 25 discharges high - pressure fluid to a manifold 195 attached to the outlet of the pump 25 . the manifold 195 ( manifold 195 a in the example shown in fig9 ) collects the fluid and directs it through an unloader valve 200 ( fig9 ) and a pressure regulator 205 before the flow passes through the hose 30 to the gun 15 . one possible arrangement of the unloader valve 200 and pressure regulator 205 is illustrated partially broken away in fig9 . returning to fig4 , a pressure line 210 provides fluid communication between the manifold 195 ( upstream of the unloader valve 200 and the pressure regulator 205 ) and the sensor aperture 155 ( fig8 ) of the idle down controller 130 . thus , the pressure applied to the piston portion 170 ( fig8 ) is substantially equal to the pressure at the manifold 195 , which is substantially equal to the outlet pressure of the pump 25 . the operation of the idle down controller 130 will be described with reference to fig3 and 4 . the user starts the engine 20 to begin operation of the pump 25 . the pump 25 draws low - pressure fluid from the source , increases the pressure of the fluid , and delivers the fluid to the manifold 195 . the user grasps the gun 15 and aims it at the surface to be cleaned , then pulls the trigger 35 to open the valve and initiate the flow of high - pressure fluid out of the gun 15 . the engine 20 operates at a desired speed during the discharge of water from the gun 15 to produce a flow of high - pressure fluid that collects in the manifold 195 and then passes through the unloader valve 200 ( fig9 ) and the pressure regulator 205 . the pressure regulator 205 reduces the pressure of the fluid to the desired operating pressure of the system . the manifold pressure is transferred to the sensor aperture 155 of the idle down controller 130 via the pressure line 210 . because there is no flow through the idle down controller 130 , little or no flow passes through the pressure line 210 . rather , the pressure simply increases or decreases with the manifold pressure . the high - pressure within the idle down controller 130 forces the actuator 145 inward against the biasing spring 140 toward the normal speed position such that the governor 60 can control the engine speed . as illustrated in fig6 , one or more washers 215 can be positioned between the shoulder portion 160 and the idle lever 125 to limit the travel of the actuator 145 as may be required to adjust the system . when the user releases the trigger 35 , a pressure increase occurs within the hose 30 and the gun 15 . the pressure increase forces the unloader valve 200 ( fig9 ) to move to an open position to bypass the high - pressure fluid from the outlet of the pump 25 to the inlet of the pump 25 . once the flow is bypassed , the pressure within the manifold 195 , 195 a drops substantially . the pressure drop is transmitted to the sensor aperture 155 of the idle down controller 130 via the pressure line 210 . the reduced fluid pressure on the system is such that the spring 140 within the housing 135 biases the actuator 145 outward to the position illustrated in fig3 and 4 . in this position , the governor 60 is biased or forced toward the idle position and the engine speed is reduced to the idle speed . the ability to reduce the engine speed when high - pressure fluid is not required reduces wear on both the engine 20 and the pump 25 . in addition , reducing the engine speed can improve the fuel economy of the engine 20 in some situations . the positioning of the idle down controller 130 results in a very simple system . the idle down controller 130 is directly coupled to the engine 20 with a single pressure line 210 between the pump 25 and the controller 130 . in addition , the operation of the controller 130 is such that the controller 130 need not be overly sensitive because the difference in pressure between the high - pressure fluid ( during discharge ) and the low - pressure fluid ( during bypass ) is typically in excess of 1000 psi . for example , many types of pressure washers operate with a manifold pressure of between about 2000 psi and 4000 psi during fluid discharge . after the trigger 35 is released and the unloader valve 200 ( fig9 ) moves to the unloaded position , the manifold pressure drops substantially , for example to about 300 psi for a 2000 psi rated pressure washer . thus , the pressure difference between the high - pressure fluid and the low - pressure fluid is about 1700 psi or greater . the large pressure difference between the two operating pressures of the system allows for the use of a less sensitive or less finely tuned idle down controller 130 , thus reducing the cost of the system . the simplicity of the system further reduces the cost of manufacturing and assembling the various components . in addition , the present device moves the engine throttle 50 to the idle position in response to a drop in pressure , rather than an increase in pressure . thus , should the pressure line 210 develop a leak or a clog , the pressure drop would likely result in the engine 20 idling rather than operating at full speed . it should be noted that while the foregoing describes the invention as being applied to an engine powered pressure washer , other constructions may be applied to motor driven pressure washers . in these arrangements , the idle down controller 130 actuates a device that is operable to reduce the rotational speed of the motor or stop the motor . for example , in one construction , the idle down controller 130 moves a switch that opens a circuit between the motor and the power supply to stop rotation of the motor . in other constructions , the idle down controller 130 moves a device that varies the flow of power to the motor . for example , a variable capacitor or a variable resistor could be employed . in still other constructions a frequency varying device is used to reduce the frequency of the electrical current provided to the motor , thereby slowing the motor . thus , the invention provides , among other things , an idle down controller 130 that responds to pressure changes within the manifold 195 to reduce the engine speed to an idle speed in response to the closure of a valve in a pressure washer gun 15 .