My Stilo jtd 115 started seriously losing power when engine under normal load, for example pulling away at a junction, hitting an incline - would'nt pull at all in 3rd or 4th gear I managed to simulate the fault repeatedly whilst driving below 30mph by knocking it out of gear, letting revs go to IDLE speed & then trying to catch it on 4th gear (low revs) on the move - no torque at all - if on an incline the car actually decelerates steadily even with foot to the floor - pumping acclerator & it does nothing at all - if on a decline - again with foot to the floor - the rpm raises extremely slow until 1800 - 2000 rpm then it takes off suddenly. Found that if I drop a gear & hence force the revs up to 2000 ish - fault is eliminated. {Corrective Action} - Removed EGR solonoid & also throttle body & cleaned out sludge & carbon. A diesel mechanic (my neighbour) told me to check the map sensor & pointed this out to me on the manifold. I deduce that if the thottle body was so badly gunged then the map sensor might be also - removed it & found that the short tube leading into sensor interior was badly clogged with carbon & sludge - so I cleaned this out with cotton bud & degreasant - car been pulling like a champion ever since.
Don't know if it was the ThrottleBody/Egr/Map sensor clean & degrease or a combo of all but it only took me a hour & a bit to do all & I'm well pleased with result.
Do as follows -First remove Egr solonoid - 4 small bolts lower ones a pig to get at (& to re-tighten), then egr ribbed pipe from valve to throttle body -taking care with the two gaskets. Secondly, remove the air intake pipe flange (Black plastic - comes up from air filter) - 3 long allen bolts. Thirdly, remove throttle body - fixed to manifold with 3 shorter allen bolts - take care of gasket! - lift out the throttle body & pull the small hose from the throttle plate actuator diaphram to allow you to completly remove TB from car. - Clean all of the above then RE ASSEMBLE exactly. All of the bolts are a pig to get to.... Last but not least, remove the single bolt securing the MAP sensor to the rear of the inlet manifold right next to the EGR solonoid (unplug first) - (Can be undone with an allen key despite being a fancy torx bolt head) - withdraw carefully & clean out he hole throughly with COTTON BUDS & DEGREASER ONLY.
CAREFUL NOT TO DROP ANY OF THE PARTS - PARTICULARLY THE TWO SMALL GASKETS FROM EGR PIPE DOWN THE BACK OF THE ENGINE.
HOPE THIS HELPS SOME OF YOU.
I'm told that other problems such as burst intercooler pipe, or bad connection at the maf sensor plug could also cause very similar symptoms.
