I am pulling my hair out with this problem, I have an 03 stilo and suffering power loss with revs below 3000. I have cleaned map sensor, replaced maf, and it's still happening, disconnected maf and it runs ok but not with full power on the default settings but having replaced maf i am Now at a loss where to go next, fuel consumption with or without maf sensor connected is not affected at average of 45 mpg, have connected to fiat scan diagnostic and no codes reported. Once car reaches 3000 goes like normal except large amounts of black smoke belches out of exhaust, as power cuts in, at idle feels like it runs lumpy, have also replaced fuel filter, air filter. All these issues seem to have started after intercooler pipe through inner wheel arch split, which was also replaced, along with the crank sensor as this became faulty, not sure if this is connected at all. Any help will be appreciated.

Do you have any knowledge of when the EGR valve was last looked at and cleaned or if it is blanked off...could be worth a clean if the valve is stuck open.
Cleaned mine other day last done 16k miles ago and was starting to stick slightly, but not too gunked up from last clean used brake cleaner spray to clean it out till nice and smooth n clean , or try blanking there are threads on egr valve and info in the guides section, if you decide to check be careful of the plastic fuel box thing to left of egr valve the fuel line attachments are only plastic and can break off if you spanner slips..done it myself so more careful when doing it this time, or you could try just blanking it...no hissing noises coming from other cracked pipework is there and you have no problem with brake light switch.
Here is one thread and many more if you search
https://www.fiatforum.com/stilo/222251-fiat-stilo-1-9-diesel-loss-power-when-accelerating.html

hi there...

the last owner had the same problem we cleaned the maf etc, but turned out to be a loose plug on the ECU, I FIND IF I DON'T LET THE IGNIGITION DO ITS CHECKS AN START IT IT WILL HAVE NOT TURBO, might be just me.

Thanks will try cleaning erg, as never done before, mileage is 105,000. Didn't think about this valve as when the MAF disconnected it runs, hence why I replaced it, would the disconnection of the maf also trick the ECU into thinking that the erg valve was working ok ? previously experienced brake light switch issue so have new switch fitted, also gives a fault code on diagnostic so I know it's not the switch this time, no obvious signs or sounds of loosing air on other pipe work now intercooler pipe replaced. Will also try the ECU connections, but I always let the checks finish before I try and start. Don't think it's turbo related as after 3000 rpm it kicks in and it's back to full power,

unplugging the MAF wont trick the ECu, all it will do is run on default values. Sounds like you need to clean the EGR or blank it off - I also suggest checking the solenoid is working correctly on the EGR because if it isn't, its pointless cleaning it as you'll need a new one (or blank it off).

Your issue does sound very symptomatic of a stuck or sticking EGR.

Should you check the egr valve and not go the blanking route when cleaned you shoud be able to push the valve in all the way and it will sping closed freely once it is clean..
a little tip is too have a good supply of those cheap gloves for hands as the black gunk is a real pain to clean out of your hands

Will try and clean the Erg valve tomorrow, reading up on the cleaning and looking at the unit itself, the bottom 2 Allen key bolts look a nightmare to get to, is it better to take the small pipe off underneath first and then split later, also would you recommend splitting the solenoid off as well or leave that connected to the valve body ?

folk have there own way of doing things I read somewhere on here think it was good tip from clivvy and remove the fuel filter behind the valve as only 2 bolts pipes on filter just clip and push fit this gives more room.I also removed pipe from black plastic ducting box to left of valve to give less chance of damage to the in/out tubes there.
I did remove the small corrugated pipe at the bottom first and just loosen the egr 3 bolts a little for extra movement first, some do not .there is small clamp at bottom of pipe and both ends have a metal washer although there is no need to get at the other awkward end until vale is out as valve and that small pipe will come out together, if you take pipe off valve is just matter of making sure it lines up before tightening at valve end then when final fitting it all fits ok, , the bottom end is little fiddle to put back on but take time and it alls goes together ok used a few dabs of copper slip to hold the metal washer in place, when putting egr back on just have the 3 bolts already in the valve as room is tight to put them in, think you said you already done the map sensor if not is good time to clean also as easy access and only one allen/torx bolt

Many thanks for everybody's help.
Have cleaned ERG valve this morning, front end was pretty clear, however valve was still sticking so removed solenoid and found it full of crud, cleaned that all out and is now nice and free, reassembled, bottom pipe was a swine but got there in the end. Good tip on the gloves. Now goes like stink , forgotten how much power/ torque these cars have got, must have been reducing my performance for a while.

Good that cleaning the valve got the power back in the motor , if you intend keeping the car and the egr working as normal and not blank it then it most probably need a clean every 24k miles to keep it working healthy, mine was only little gunked up after 16k but is more the sticking of the valve inside the unit that causes problems.And now done once is always that much easier next time with that bottom pipe connection, fingers crossed it keeps chugging along for you, unless the solenoide part decides to give up and then just a quick cheap blanking plate will sort it..you may get some extra black smoke for short time as engine settles and the extra flow through valve clears any soot about that area.
And if the MAF was not the item causing lack of power least you got a spare close at hand , talking of hands you be looking like you been living in the woods for the next 2 weeks trying to clean the black gunk out of them

Noticed the extra Blake smoke, hands ok got supply of disposable gloves before I started but the lawns taken a beating, only issue is the mpg is all over place on display at moment with new Maf hopefully now all working correctly it will settle, would you recommend an ecu reset and start again with the maf

Which mpg readings are you going by on dash, the average or mpg at that moment in time as that one does go random depending on driving state use of throttle hill or downhill etc.
A ecu reset would do no harm I do not know exact way on that or if it would help the dash readings for mpg ,only have knowledge on disconnecting battery for 30 mins.for resetting ecu's

Going on average mpg reading from dash, maf instruction on fitting was the 30 mins battery disconnect for the reset, then advised that ecu could take approx 30 miles to adjust to new settings. Don't surpose it will hurt so I'll give it a go.

if MAF instruction advise disconnecting battery to reset I would follow that advice, and if not using car overnight just connect back up in morning .
Yes also the 30 mile part sounds right too if not a little longer as I now remember from various posts that can take time for the ecu's to relearn various fuel settings, and would presume having a new maf that would make it more likely and would certainly give the car some time to adjust and learn the various new input signals and fuel management

Just done that, will reconnect in morning, will let you know if there is any improvement.

Fuel consumption on the up, still not brilliant but only done about 15 miles on short runs so far, will continue to see if I get an improvement on a longer run at the weekend . Thanks again for all advice and help given

Least the fuel numbers are heading in right direction, and like you say 15mile run will not give you a decent read on the mpg as some of those miles will also be engine coming up to working temp, more so being a diesel, if you take for longer more steady drive when you get to your cruising speed just reset the "B" trip this will give you idea of the mpg if holding that speed for a few miles, though in the whole I do not know how acurate the mpg reads given actually are when compared to the old fashion way of fuel put in miles travelled maths, would think once you done 100 miles you get an idea and need to take into account if you live in rural or uraban area and type of driving being done for the mpg reads also, but least an improvement and hope is sorted now

Mpg now looking food, 150 mile trip around Wales gave me average of 51.5 mpg, now week later 388 miles giving me average of 48.5. Shame the urban driving and short trips pulling it down.