Have a Throttle return spring arrangement or diagram?

First off you would need to find out which of these systems are triggering that message .

• Starting Disabled (Due To Electronic Throttle Control)
• Starting Disabled (Due To Theft System)

Is the car an padlock symbol lit in the instrument cluster ? Seeing how you have the reduced engine power message I would say your problem lies in the electronic throttle control .

Reduced Engine Power: Refer to Throttle Actuator Control (TAC) System Description in Engine Controls - 3.6L or Throttle Actuator Control (TAC) System Description in Engine Controls - 3.8L

The throttle actuator control (TAC) system is used to improve emissions, fuel economy, and driveability. The TAC system eliminates the mechanical link between the accelerator pedal and the throttle plate. The TAC system eliminates the need for a cruise control module and idle air control motor. The following is a list of TAC system components:
• The accelerator pedal assembly includes the following components:
- The accelerator pedal
- The accelerator pedal position (APP) sensor 1
- The APP sensor 2
• The throttle body assembly includes the following components:
- The throttle position (TP) sensor 1
- The TP sensor 2
- The throttle actuator motor
- The throttle plate
• The engine control module (ECM)
The ECM monitors the driver demand for acceleration with 2 APP sensors. The APP sensor 1 signal voltage range is from about 0.98-4.16 volts as the accelerator pedal is moved from the rest pedal position to the full pedal travel position. The APP sensor 2 range is from about 0.49-2.08 volts as the accelerator pedal is moved from the rest pedal position to the full pedal travel position. The ECM processes this information along with other sensor inputs to command the throttle plate to a certain position.
The throttle plate is controlled with a direct current motor called a throttle actuator control motor. The ECM can move this motor in the forward or reverse direction by controlling battery voltage and/or ground to 2 internal drivers. The throttle plate is held at a 7 percent rest position using a constant force return spring. This spring holds the throttle plate to the rest position when there is no current flowing to the actuator motor.
The ECM monitors the throttle plate angle with 2 TP sensors. The TP sensor 1 signal voltage range is from about 0.5-4.25 volts as the throttle plate is moved from 0 percent to wide open throttle (WOT). The TP sensor 2 voltage range is from about 4.45-0.7 volts as the throttle plate is moved from 0 percent to WOT.
The ECM performs diagnostics that monitor the voltage levels of both APP sensors, both TP sensors, and the throttle actuator control motor circuit. It also monitors the spring return rate of both return springs that are housed internal to the throttle body assembly. These diagnostics are performed at different times based on whether the engine is running, not running, or whether the ECM is currently in a throttle body relearn procedure.
Every ignition cycle, the ECM performs a quick throttle return spring test to make sure the throttle plate can return to the 7 percent rest position from the 0 percent position. This is to ensure that the throttle plate can be brought to the rest position in case of an actuator motor circuit failure. Observe, under cold conditions, the ECM commands the throttle plate to 7 percent with the ignition ON and the engine OFF to release any ice that may have formed on the throttle plate.

The first thing to do would be to hook up a professional scan tool ,check codes an live data .

Most carburetors have more than one opening on the throttle lever. Connect your throttle cable to one of these openings. With the throttle closed, find a location that you can connect a modified bracket to. Secure your throttle cable to this bracket. Connect a return spring so that it will return the throttle plates in a closed position. To check if all is ok, look down the throttle bore to make sure the plates are closed. Open and shut the throttle lever to make sure everything is working and not sticking open.

Clean the throttle plate an bore ! Video's on youtube .

You don't say what make an model vehicle ! But with most vehicle makes it has to do with the Throttle Actuator Control (TAC) System , electronic throttle control ! are you having reduced engine power ? There are probably DTC'S - diagnostic trouble codes stored in the PCM - engine computer .
The throttle actuator control (TAC) system is used to improve emissions, fuel economy, and driveability. The TAC system eliminates the mechanical link between the accelerator pedal and the throttle plate. The TAC system eliminates the need for a cruise control module and idle air control motor. The following is a list of TAC system components:
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The accelerator pedal assembly includes the following components:

-
The accelerator pedal

-
The accelerator pedal position (APP) sensor 1

-
The APP sensor 2

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The throttle body assembly includes the following components:

-
The throttle position (TP) sensor 1

-
The TP sensor 2

-
The throttle actuator motor

-
The throttle plate

?€¢
The engine control module (ECM)

The ECM monitors the driver demand for acceleration with 2 APP sensors. The APP sensor 1 signal voltage range is from about 0.98-4.16 volts as the accelerator pedal is moved from the rest pedal position to the full pedal travel position. The APP sensor 2 range is from about 0.49-2.08 volts as the accelerator pedal is moved from the rest pedal position to the full pedal travel position. The ECM processes this information along with other sensor inputs to command the throttle plate to a certain position.
The throttle plate is controlled with a direct current motor called a throttle actuator control motor. The ECM can move this motor in the forward or reverse direction by controlling battery voltage and/or ground to 2 internal drivers. The throttle plate is held at a 7 percent rest position using a constant force return spring. This spring holds the throttle plate to the rest position when there is no current flowing to the actuator motor.
The ECM monitors the throttle plate angle with 2 TP sensors. The TP sensor 1 signal voltage range is from about 0.5-4.25 volts as the throttle plate is moved from 0 percent to wide open throttle (WOT). The TP sensor 2 voltage range is from about 4.45-0.7 volts as the throttle plate is moved from 0 percent to WOT.
The ECM performs diagnostics that monitor the voltage levels of both APP sensors, both TP sensors, and the throttle actuator control motor circuit. It also monitors the spring return rate of both return springs that are housed internal to the throttle body assembly. These diagnostics are performed at different times based on whether the engine is running, not running, or whether the ECM is currently in a throttle body relearn procedure.
Every ignition cycle, the ECM performs a quick throttle return spring test to make sure the throttle plate can return to the 7 percent rest position from the 0 percent position. This is to ensure that the throttle plate can be brought to the rest position in case of an actuator motor circuit failure. Observe, under cold conditions, the ECM commands the throttle plate to 7 percent with the ignition ON and the engine OFF to release any ice that may have formed on the throttle plate.

Binding or friction in the throttle cable attachment to the throttle body if fuel injected, or to the carburetor throttle assembly. Spray it down with carburetor cleaner-all around the outside and inside where the throttle valve or valves are- and work it back and forth by hand. A coiled spring on the throttle valve assembly (where the cable attaches) should return the throttle to idle setting with no binding.

The spring or wire that connects your pedal to the throttle body may broken or damaged. Check under your hood and look at the throttle body (it's the carburetor looking thing). There should be a steel wire connected to it coming from the back of the engine bay. It should connect on the side where you'll see a few springs. If nothing looks broken there, turn the part of the throttle body connected to the spring and wire. If it revs up when you move it, then the cable could be broken somewhere between there and the gas pedal.

Alternatively, the linkage on the pedal could have been disconnected some how. Check behind and above the gas pedal to see if eveything is connected properly.

Return spring too weak. Replace throttle return spring, lubricate throttle cable / linkage.

The spring that controls the throttle cable on a car is called a throttle return spring or a throttle-valve spring. This helps determine the position of the throttle cable and controls its pressure.
Poor fuel mileage is when a vehicle uses excessive amounts of fuel in order to travel far.



------------------2012.9 MB SD Connect Compact 4 Star Diagnosis

There is no carburetor on any of the 6 cylinder or 8 cylinder Jeep Grand Cherokees. They have Fuel Injection and a throttle body which looks like a carburetor scaled down.

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Instructions on how to remove and replace the throttle body follow:

Throttle Body REMOVAL & INSTALLATION

1. Disconnect the negative battery cable.
2. Remove the vacuum hoses from upper bonnet, unfasten the retaining clips and remove the upper bonnet assembly.
3. Remove the lower bonnet retaining bolts and lower bonnet.
4. Remove the throttle cable and the return spring.
5. Disengage the wire harness connector from the injector.
6. Disengage the wire harness connector from the WOT switch, ISA motor and TPS.
7. Disconnect the fuel supply and return lines from the throttle body.
8. Tag and disengage the vacuum hoses from the throttle body assembly.
9. Disengage the potentiometer wire connector.
10. Loosen throttle body retaining bolts and remove throttle body assembly from the intake manifold. To install:
    
11. Clean the intake manifold and throttle body mating surfaces of old gasket material.
12. Install a new gasket and the throttle body assembly. Tighten the mounting bolts to 16 ft. lbs. (21 Nm).
13. Engage the potentiometer wire connector.
14. Engage the vacuum hoses to the throttle body.
15. Engage the fuel lines to the throttle body.
16. Engage the WOT switch, ISA motor, TPS, and injector electrical connections.
17. Install the return spring and throttle cable.
18. Install the lower bonnet and fasten the retainers.
19. Install the upper bonnet assembly, retaining clips and vacuum hoses.
20. Connect the negative battery cable.
21. Start the vehicle and check for fuel leaks. Fig. 1: Exploded view of the throttle body and related components
    

WELL IT TURNS OUT YOU NEED TO ROTATE THE SPRING TWO ROTATIONS AND CLIP IT TO THE THROTTLE PLATE THAT ATTACHES TO THE THROTTLE CABLE