Fixed the issue with mine
2008 185bhp D5 Auto 150kmiles!
Swirl Flap arm detached (has been for +2yrs) was causing the following fault codes and temporally putting the car into a low power mode - the engine fault light did NOT come on even though the codes had been recorded - re-attaching the arm with a bodge to keep it in place, cleared the codes and all good for the last 5days !
Fault codes as reported by a friends Foxwell code reader (not DiCE),
my cheap ODB2 reader didn't return any codes!
- P010116 Mass or volume air flow circuit range/performance, general electrical failures, circuit voltage below threshold
- P201500 Intake manifold runner position sensor/switch circuit range/performance - (aka Swirl Flap)
I will post the VIDA summary of these codes when I'm back home, as under the P010116 MAF fault code diagnostics it said check the swirl flap linkage so this is a known issue relating to the 2 systems (in my case under high rev's)
Symptoms:
When accelerating normally no issues and the car would pull normally, lots of power and rev to the red line.
But, if I held the rev's at about 3,000rpm for a slightly longer period (>30sec's or so) ether whilst stationary or driving, it would temporarily go into a low power mode every time, and would then limit the rev's to 4,100rpm max.
If you backed off and let the revs drop below 2,000rpm it would clear the issue
Probably one of many causes of the engine going into the 'low power mode', but hope this helps someone....
The key thing for me is the fact that fault codes had been recorded even though the engine fault light had not come on, and these codes could not be read back by a basic ODB2 reader - once I was able to access these codes it made diagnoses 100% easier