I have a 2004 mercury mountineer the servce engin light has come on and the engin fail safe mode. i had a test done on it and it says throttle actultor dontrol system could you please tell me what that means

you have serious engine or transmission problems and it is placed in limp home mode
check water levels , oil levels, overheating both engine and transmission

Failure Mode Effects Management (FMEM) is an alternate system strategy in the PCM designed to maintain engine operation if one or more sensor inputs fail.
When a sensor input is perceived to be out-of-limits by the PCM, an alternative strategy is initiated. The PCM substitutes a fixed value and continues to monitor the incorrect sensor input. If the suspect sensor operates within limits, the PCM returns to the normal engine operational strategy.
All FMEM sensors display a sequence error message on the scan tool. The message may or may not be followed by Key On Engine Off or Continuous Memory DTCs when attempting Key On Engine Running Self-Test Mode.
With the fail safe mode was the "Service" wrench light lit or check engine light ?
With

wrench panel warning light on.

Fail safe is TPS sensor. When you go in fail safe the vehicle give a set amount of RPM and no throttle response the rule of thumb in fail safe is APP1 and APP2 does not agree the goal is to protect the catalytic convertor. So if the transmission was at fault you dont over rev to end up burning the Cat. Or over rev to break the engine It all boils down to a throttle body assembly as the solution

Try having the codes cleared, and see what happens.

Now you have to stop using it,sorry

You have two main Fail Safes
One is overheating
Yours is IGNITION COIL MISFIRES

Without getting in a long technical story
the individual coils you have COP Ignition System,
either slowly fail and set no light,or set a code
In your case it doesn't matter because the codes won't help much

You most likely have a really bad ignition coil
It does not ground out as it should in the PCM (computer)
That spike comes back on the TPS Sensor (throttle position)
and then you lose the TPS normal Data that is the result
of where you push on the gas pedal

At that point there is no way to adjust fuel injector pulse,so
it starts killing cylinders and eventually goes into ETC Fail-Safe

Your Done-- Also there may not be many professionals that
will believe me. Been there done that.

Ideally a shop that actually uses an oscilloscope can solve
which coil is bad
You can buy 1 coil for $60.00 & walk it from one cyl
to the next and after a week fix it for $60.00

I will tell you, people have spent $3000.00 at dealers
& got zip.

In the event my story if off,
your next problem would be the
TACM (throttle actuator control motor )
That will be your codes. Do Not let the codes
guide you or your repair shop. The throttle body
is $700.00. If you do need one, you better be installing
your self.

I understand all you said

Without the vehicle and a fresh
diagnostic approach, I personally
don't think any internet ideas will help

You still have misfires, that are spiking the PCM &
TACM on the throttle body and putting it
into ETC Fail Safe.

pulls codes first auto zone checks for free

I encountered the same problem, my engine fail safe mode light came on and shut the car down. I took my car to my mechanic and he found the solution to the problem. The car needed a throttle body cleaning and the fuel filter needed to be replaced. After having my truck serviced my mileage increased from 14.6 mpg to 15.4 mpg
ENGINE FAILED SAFE MODE WARNING LIGHT, GONE Total cost $86.45