When driving and i step on the gas, as soon as i hit 40mph the car kick up like a jerkin motion then run smoothly till i stop. it a used a6 2001 100k, jus bought it first car, so am a newbie

a 35year old car. never seen one me with less than 10 problems.
100% expected. USA car in OK state clearly told and nice!
NO ENGINE TOLD (size) car is called N13 you generation car.
auto tranny and with 4wd?
USA PULSAR NX, IS 1.6L DOHC OR SOHC ENGINE.
ALL ARE INTERFERENCE ENGINES,
NEVER IGNORE THE TIMING BELT . REPLACE IT FIRST.
so is and engine problem, not transmission failure to up shift, correct>? this fact must be learned first. or off base tests go.
engine Power loss has 50 causes. (electric or pure mechanical)
but in basic engine theory (ASE) and gas engines, and otto cycle engines,
the ordered list is.
1: good engine. . EGR not stuck open. CAM BENT NOT BAD OR WORSE SLIPPING. << FAST DRIVING THIS WILL Bring destruction.
2: good spark ,cap, rotor , HV spark wire set and plugs.
when 40mph cliff of failure hits, is engine misfiring? violently?
or is power loss smooth loss of power, RPM fails to rise more. but falls.
the former is spark bad. (ckp ,cmp or caused by cam belt slip)
#3 fueL
if slow smooth power loss,fuel pressure may be low.
if slow gee? the belt on the cam slips. never drive like that.
day one traded to this car, the belt is first ( I just hate bent valves)

And you had all the data looked at with a scan tool
& road tested or your just discussing the what if's?

Vehicle Preventative Maintenance Log Book ?

Just drive & never work on it ?

scan car for any codes or unplug computer a few times then see if issue goes--its under the dash or engine area--may need a update on trans-they du a data stream w factory gear to pinpoint problem then download new info

Check the fuel pump and plugs{coil}

Might have to reset the codes on the computer. Take the + battery cable off the battery and reconnect it afer 5 minutes. Next try to start the engine without holding the gas petal down, it should start and run rought till the computer resets itself. If engine stops, restart the engine and hold the gas petal down and give it enought gas so it will run smooth, it may take 5 minutes or so for it to smooth out and run at idle speed. If this did not fix the problem, check for a vaccum hose that may be off some where on the engine

I would change the fuel filter that would be the first thing and go from there

Turbo is not boosting

Sounds like a range sensor problem! It mite be bad and need changed! About $80 for the part, versus $180 for ford to put it on!

I would replace that tank (asap), so there can be a cap back on it.
With the cap off, the fuel system can't build up any pressure to hold the gas in the lines.