Sluggish, slow, engine low power

Hi,

I recently bought list car from an auction. The car has a lumpy idle and shakes ever so slightly like it has a misfire. It is under powered, sluggish and the throttle response is pretty shocking too. The car will struggle to hold a steady rpm. For example. I will take it up to 1,500 rpm and hold the throttle still, but the rpm will drop.

Earlier today I plugged in a code reader. It does not support Peugeot but I was able to access the live data. Eg: Rpm, oil temperature, coolant temperature etc. And noticed something called

LTFT (long term fuel trim)

and

STFT (short term fuel trim)

The STFT was fluctuating quite a lot with a wide range. I have no idea what it is, but googled what they should be. As far as I am aware the LTFT should be anywhere from 12% to 14% Where as the LTFT on my Peugeot is at a constant 0.78%.

I also read that the STFT should be 6% of the LTFT or something a long those lines. But instead it is all over the place constantly fluctuating on idle to and from 0.00%, 3.12%, 0.078%, 2.34%, -1.57%, -0.75%.

When the engine is revved the STFT jumps to 11.71% and the LTFT stays at a constant 0.78 when revved and on idle. It does not change.

As far and I am aware this means the car is compensating for something, creating a rich mixture. Am I right in thinking that it could be any of these?

Maf or O2 sensor fault, Intake gasket leaks, cracked inlet or split hoses, clogged or dirty fuel injectors, fuel delivery issues or exhaust restrictions such as a clogged catalytic converter?

Originally I thought I might have an inlet leak not only because its plastic, but because if you stab the throttle there is a fluffing sound from the inlet and then it revs immediately afterwards, but delayed. There is also a rich exhaust smell coming from the engine bay.

My theory was then ruled out when I read that if you hold the rpm at a steady 2500 and the STFT immediately decreases and goes down to an acceptable level and the LTFT starts to go down too, that, that means you have an air leak. Whereas my LTFT stays at 0.78 no matter what and the STFT rises a as high as 11.71%.

From this data could anyone please narrow down what it could be? I am stumped. I do not want to throw money at the car, going out and buying loads of different parts until I find the problem.

Thanks for your help and expertise.

Kind regards,
Ben.