2.5V6 Mondeo speed can not exceed 50 even if accelerate

Cruise control only maintains speed by utilizing the accelerator. To speed up it increases it and during slowing is removes it. The cruise control will not apply brakes in the event of a steep downhill run. In this case the vehicle will start to accelerate in the same manner as if the cruise control was not engaged. But in theses cases, most cruise controls, once the speed exceeds a certain amount above the set speed, will auto-disengage as a safety feature.

no make , model or year mentioned so , guessing it is a car less than 10 years old , run the fault codes to find the problem area

Some cars are fitted with a speed reminder setting. If you exceed the speed that has been entered then an alarm sounds. Maybe a previous owner has set it at 50mph. You can drive at any speed but the reminder will beep if you exceed its' setting. Not saying you definitely have one fitted but might be worth googling or contacting a Toyota dealer.

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

Sounds like a vacuum leak. Or manifold leak.

it could be the coil pack, its one of the symptoms that can happen when they fail, if it has a crack or seal broken damp can get inside and cause it to not work properly.

Next time the engine light comes on, get the codes pulled and get back to me

throghout bearing

split intercooler hose, happened to mine do you hear a sucking noise when accelerating? new hose costs about 40 quid main dealer only