Cruise control won't hold speed

The cruise control system in Carmy has cruise constant speed, cruise acceleration, cruise deceleration and other functions.
Source: https://www.wapcar.my/cars/toyota/camry

It is HVAC 1fuse #39 in the rear fuse block ,this powers the on/off switch for cruise control ! Fuse Block - Rear Beneath the left rear seat. What engine does it have ? 4.2 L or 5.3 l There is no vacuum involved in the operation of the cruise control ! Your vehicle has electronic throttle control .
Cruise control is a speed control system that maintains a desired vehicle speed under normal driving conditions at vehicle speeds above 40 km/h (25 mph). Steep grades may cause variations in the selected vehicle speeds.
The following are the main components of the Cruise Control System:
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The powertrain control module (PCM)

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The On/Off switch

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The Resume/Accel switch

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The Set/Coast switch

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The TCC brake switch

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The stop lamp switch

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The throttle actuator control (TAC) motor

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The vehicle speed sensor

Cruise Control Engaged
The cruise control system will engage and adjust the vehicle speed based on the activation of the following cruise control switches:
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On/Off

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Resume/Accel.

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Set/Coast

The cruise control switches are located on the multifunction/turn signal lever.
The powertrain control module (PCM) monitors the signal circuits of the cruise control switches in order to determine when to capture and maintain the selected vehicle speed. The PCM uses the throttle actuator control (TAC) module motor in order to control the vehicle speed. For further information on the TAC System, refer to Throttle Actuator Control (TAC) System Description in Engine Controls - 4.2 L.
Ignition positive voltage is supplied from the 10 ampere HVAC 1 fuse to the cruise control switch via the ignition 3 voltage circuit. When the normally open cruise control On/Off switch is turned On, the switch closes and the PCM detects a high signal voltage on the cruise control on switch signal circuit. When the normally open Set/Coast switch is pressed, the switch closes and the PCM detects a high signal voltage on the cruise control set/coast switch signal circuit. To engage the cruise control system, turn the On/Off switch On and momentarily press the Set/Coast switch. The PCM will confirm that the cruise control enable criteria has been achieved. The PCM will engage the cruise control system and record the selected vehicle speed. The PCM sends a class 2 message to the instrument panel cluster in order to illuminate the cruise control indicator. Pressing the accelerator pedal, while the cruise control system is engaged, will allow the driver to override the cruise control system in order to accelerate the vehicle beyond the current set vehicle speed. When the accelerator pedal is released, the vehicle will decelerate and resume the current set vehicle speed. The driver can also override the current set vehicle speed via the Set/Coast switch and the Resume/Accel switch. When the cruise control system is engaged, pressing and holding the Set/Coast switch will allow the vehicle to decelerate from the current set vehicle speed without deactivating the cruise control system. When the Set/Coast switch is released, the PCM will record the vehicle speed and maintain the vehicle speed as the new set vehicle speed. When the cruise control system is engaged, momentarily pressing the Set/Coast switch will allow the vehicle to decelerate at 1.6 km/h (1 mph) increments for each time that the Set/Coast is momentarily pressed, with a minimum vehicle speed of 37 km/h (23 mph). When the normally open Resume/Accel switch is activated, the switch closes and the PCM detects a high signal voltage on the cruise control resume/accel switch signal circuit. Activating and holding the Resume/Accel switch, when the cruise control system is engaged, will allow the vehicle to accelerate to a greater vehicle speed than the current set vehicle speed. When the Resume/Accel switch is released, the PCM will record the vehicle speed and maintain the vehicle speed as the new set vehicle speed. When the cruise control system is engaged, momentarily activating the Resume/Accel switch will allow the vehicle to accelerate at 1.6 km/h (1 mph) increments for each time that the Resume/Accel switch is momentarily activated, with the maximum acceleration total of 16 km/h (10 mph) over the current set vehicle speed . Momentarily activating the Resume/Accel switch, after the cruise control system has been disengaged by pressing the brake pedal, will recall the previous set vehicle speed that is recorded in the PCM.

Bummer deal! This may be a way to tell you some tail lights are burnt out. Some cruise controls have a fuse in a second location.
The fuse is not in right or is blown. Check with a new fuse. Hope this helps. ...gc http://www.auto-tune-up-and-repair-options.com/

Cruise Control
Any given speed above approximately 22 mph (35 km/h) can be maintained with the cruise control by operating the lever.
-see photo

1. Accelerate and set: Lift lever briefly to set speed. Hold lever up to accelerate.
2. Decelerate and set:
   Depress lever briefly to set speed. Hold lever down to decelerate.
   Normally the vehicle is accelerated to the desired speed with the accelerator. Speed is set by briefly pushing
   the lever to position 1 or 2. The accelerator can be released. The speed can be increased (e.g. for passing)
   by using the accelerator. As soon as the accelerator is released, the previously set speed will be resumed automatically. If a set speed is to be increased or decreased slightly, e.g. to adapt to the traffic flow, hold lever in position 1 or 2 until the desired speed is reached, or briefly tip the control lever in the appropriate direction for increases or decreases in 0.6 mph (1 km/h) increments. When the lever is released, the newly set speed remains.
3. Canceling

To cancel the cruise control, briefly push lever to position 3.
When you step on the brake or the vehicle speed drops below approx. 22 rnph (35 km/h), for example when driving upgrade, the cruise control will be canceled.
4. Resume
If the lever is briefly pushed to position 4 when driving at a speed exceeding approx. 22 mph (35 km/h), the vehicle resumes the speed which was set prior to the cancellation of the cruise control. The last memorized speed is canceled when the key in the steering lock is turned to position 1 or 0.
Note:
If the engine does not brake the vehicle sufficiently while driving on a downgrade, the speed you set on the cruise control may be exceeded and you may have to step on the brake pedal to slow down.
As soon as the grade eases, the cruise controlled speed will again be maintained as long as the brakes were not previously applied, or the lever may be used to resume the previously set speed if the brakes were applied.


http://www.benzworld.org/forums/attachments/w202-c36-c43/153145d1197313761-pdf-owners-manual-w202-1995-2000-1999-c280_owners_manual.pdf

Once you have turned your cruise control on accelerate to desired speed press SET button on right hand side of steering wheel before lifting foot from accelerator, then remove foot from accelerator. pushing RESUME button will deactivate cruise control without turning it off. Then when clear of traffic push resume again to activate cruise control. It will automatically resume to previous set speed.

Could be the problem; however it is more likely to be under the hood where the cruise actuator is located - check the electrical connections on the actuator and the linkage between the actuator and the accelerator lever on the engine. Also, if the cruise control uses a diaphragm to control the accelerator, it may be leaking or the vacuum line to it may have fallen off - check the vacuum at the actuator with the engine running.

Possibly a broken wire in the steering column. Wires goint through the steering column for the cruise are so fragile when the tilt is used alot causing the wires to brake. Part is $70.00 through advance auto. Cheapest I've found if you order online.

Here is the OBD2 emission system drive cycle test procedure.
Engine coolant temp must be below 70c (158f) before starting the engine for either the first or second trip
The fuel level should be less than 1/2 full
First trip:
Start engine, idle for at least 1.5 minutes
Drive 3 minutes, hold b/f schdl: 1.5-2.0 msec, selector lever "3rd" eng rpm 1,800-2,000 A/C switch:ON Hold the recommended b/f schdl range. Allow road speed to vary as necessary.
Drive at 55-65 mph for 1.5 min b/f schdl 2.0-3.2 msec, selector lever "5th" Engine rpm 2,200-3,000
IGN "off" for at least 10 seconds (not more than 5 min)
Dive at 50-60 mph for 3 minutes Selector lever "4th" keep engine speed above 3,000 rpm Allow speed to vary if necessary. Do not decelerate for more than 3 consecutive seconds. A/C switch ON.
Drive at a steady state cruise of 53-58mhp b/f schdl more than 1.8 msec selector lever "5th" eng rpm 2,400-2,600
Downshift to "4th" and decel more than 5 seconds without breaking, then idle for 1 minute.
Drive two minutes b/f schdl less than 2.0 msec Accelerate to 41 mph, decelerate to 34 mph, accelerate to 41mph. Do not completely release the accelerator. A/C switch off.
Idle 1 minute in park or neutral
Drive two minutes Steady state cruise at 31-44 mph. Selector lever "4th" A/C switch OFF. Hold the accelerator pedal as steady as possible. Allow speed to change if necessary.
End of first trip. Turn the key off the begin the second trip.
Second trip:
Start engine, idle for at least 1.5 minutes
Drive 3 minutes, hold b/f schdl: 1.5-2.0 msec, selector lever "3rd" eng rpm 1,800-2,000 A/C switch:ON Hold the recommended b/f schdl range. Allow road speed to vary as necessary.
Drive at 55-65 mph for 1.5 min b/f schdl 2.0-3.2 msec, selector lever "5th" Engine rpm 2,200-3,000
IGN "off" add four gallons of fuel
Dive at 50-60 mph for 3 minutes Selector lever "4th" keep engine speed above 3,000 rpm Allow speed to vary if necessary. Do not decelerate for more than 3 consecutive seconds. A/C switch ON.
Drive at a steady state cruise of 53-58mhp b/f schdl more than 1.8 msec selector lever "5th" eng rpm 2,400-2,600
Downshift to "4th" and decel more than 5 seconds without breaking, then idle for 1 minute.
Drive two minutes b/f schdl less than 2.0 msec Accelerate to 41 mph, decelerate to 34 mph, accelerate to 41mph. Do not completely release the accelerator. A/C switch off.
Idle 1 minute in park or neutral
Drive two minutes Steady state cruise at 31-44 mph. Selector lever "4th" A/C switch OFF. Hold the accelerator pedal as steady as possible. Allow speed to change if necessary. I especially like the part where they want you to add four gallons of fuel. Not three gallons, not five gallons, four gallons. Gotta love those Nissan engineers. ...and of course they state that if the trace is not followed exactly (i.e. you botch the acceleration/deceleration) you have to start all over again from scratch

cruise controls are funny things
you have to accelerate to a speed then turn it on and press set
It will cruise at that speed
if you touch the brake it will unset and you will have to press on the accelerator again to the speed and pres resume
if you want to accelerate to pass just press the accelerator until you have passed , then just take your foot off the accelerator and it will coast until the set speed
if you change gears , it will unset
if you touch the brake , it will unset
if you have it set and find the speed to fast , hold the set button and it will slow down to the speed you want
let the button go and it will set at the speed
if you want to go faster than the set speed press the resume button and it will speed up until you get the speed you want
from your description of the problem , it appears that you have misread the instructions in the owners manual

Generally... There is ON/OFF - SET - ACCELERATE/RESUME, COAST/DECELERATE. Cruise is available at speeds above 35mph or so. Sometimes there is no main on/off. Cruise on a turn signal stem has a button that pushes in on the end, push when at desired speed. resume/accelerate slides to right, is spring loaded and return left when released. the same lever when slid left is coast/decelerate. Momentarily sliding accelerate and releasing increases crusing speed by a couple mph. If brakes are used cruise disengages, sliding resume returns you to cruise speed after braking. Coast/decelerate disengages cruise, when at desired lower speed hit set. On some, hitting set not needed, when coast is released speed is maintained. Variations may be up/ down instead or may be steering wheel face mounted. Please rate answer. Duct tape is like the force, it has a dark side.. a light side.. and holds the universe together!