C5 X7 acceleration

[osx]

I have started noticing recently that when I try to accelerate the car will initially hesitate or even slow down before accelerating. This happens with the cruise control too and a couple of times the cruise control disengaged while on the motorway. Feels like it kicks down a gear but its a manual gearbox. Idling is also rough - revs drop briefly.
Will run a diagnostic tomorrow. Could this be the EGR valve?

[GiveMeABreak]

No point in guessing at this stage - any issue with the engine management can cause this - and disengagement of cruise is automatically done by the engine ECU when there is any hesitation.

Could be a sensor, electrovalve to the EGR, air or fuel issue, so pop the codes up when you've run the diagnostic.

[osx]

Faults were under injection/ignition.

INJ : injection/ignition
State of the ECU: DCM34
Faults present : 3

P1671 : cruise control
Characterisation : information incoherent
Status : intermittent .
Location : distant .
Variables associated with the fault
Engine speed : 2240 rpm
battery voltage : 14.36 Volt(s)
ESP request status : No
gear ratio : ratio 6
measured fuel pressure : 1382 bars
accelerator pedal position : 33 %
accelerator pedal 1 voltage : 305 mVolts
accelerator pedal 2 voltage : 152 mVolts

P0088 : fuel pressure regulator control
Characterisation : rail pressure too high
Status : intermittent .
Location : local .
Variables associated with the fault
Engine speed : 2240 rpm
battery voltage : 14.36 Volt(s)
Engine status : Engine running
coolant temperature : 71 °C
fuel temperature : 25 °C
Gross measured fuel pressure : 1461 bars
measured fuel pressure : 1510 bars
HP pump flow regulator current : 833 mA

P1351 : Preheating relay circuit
Characterisation : relay controlled and spark plugs not supplied
Status : Permanent fault
Location : local .
Variables associated with the fault
Engine speed : 1120 rpm
battery voltage : 11.24 Volt(s)
Engine status : Engine running
coolant temperature : 8 °C
measured fuel pressure : 275 bars
accelerator pedal position : 0 %
supply voltage 1 : 4.99 Volt(s)
supply voltage 2 : 5.01 Volt(s)

[GiveMeABreak]

I would ignore the P1671 Cruise Control fault, as that is a likely consequence of the main fault that is P0088. Also ignore the P1351 - that is the standard Pre-Heating circuit that most HDis have most of the time.
So a few pointers for you to check - as per the fault descriptor:

Fault Code: Fault code P0088 Description of Fault: High pressure fuel regulation: The measured rail pressure is too high in relation to the set point. The ECU detects a difference of 180 bars to 250 bars for 3 to 6 seconds between the rail pressure set point and the measured rail pressure. Conditions for Fault to clear: Driving for 5 minutes with several full load accelerations for 10 seconds. Downgrade Modes whilst Fault is active: Deactivation of processing of the accelerometry Deactivation of the accelerometry strategies Deactivation of the detection of loop difference on the fuel flow rate regulator Deactivation of the injector flow rate correction strategy Symptoms: Jerking/stalling Unwanted acceleration Noise Smoke from the exhaust Lack of power Starting problem Suspect Areas: Engine ECU (Software not up to date) Poor fuel or polluted fuel (petrol, deposit, etc.) Problem on the fuel low or high-speed circuit (hose, tank, diesel fuel filter, etc.) Fuel injectors Engine fuse box Electrical harness Connectors High pressure fuel pump Fuel high pressure sensor

[osx]

From the suspected areas

Engine ECU (Software not up to date) --> probably not relevant
Poor fuel or polluted fuel (petrol, deposit, etc.) --> have been using a diesel additive for the last year
Problem on the fuel low or high-speed circuit (hose, tank, diesel fuel filter, etc.) --> air bubbles in the circuit?
Fuel injectors -->
Engine fuse box --> replaced this year
Electrical harness
Connectors
High pressure fuel pump -->
Fuel high pressure sensor -->

[GiveMeABreak]

So go for an Italian tune up with some heavy accelerations - as suggested to see if that will clear it up. It may be a bit of grot in the tank that has got in - when did you last have the fuel filter changed?

[osx]

Changed fuel filter in Aug and I run the engine at 4000rpm 5-10min every week.