D19 - S40/V40 to 2004 V40 1.9D 2001 power loss below 2500 rpm

[2001V40D]

Well, like quite a few others here I am with this V40 that is refusing to behave normally. All appears to have started after a cambelt replacement (which also appears to be a typical starting point for V40 diesel power loss issues).

Symptom history:

1. Acceleration hesitance at ~ 2500 rpm, ~ 55-60 mph
2. Very weak power on all gears below < 2500 rpm
3. Weak power on 3rd and 4th gears < 2500 rpm

Above 2500 rpm, turbo kicks in and the car takes off.

On the highway, driving 60-70 mph, cruise control is pretty useless because at gear 5 you end up in the 2500 rpm and there it gradually drifts until it shuts off. Before everything started, cruise control was running solid.

Error codes when it all began:

ECM-0000 One of: (don't know which)

ECM-0000 Engine speed (RPM) sensor. Faulty signal. Intermittent fault
ECM-0000 Impulse sensor. Faulty signal, Intermittent fault.
ECM-0000 Impulse sensor. Signal too high, overspeeding.
ECM-0000 Impulse sensor: Signal faulty. Permanent fault.

ECM-1804 Boost pressure sensor. Signal too high
ECM-180C EGR position sensor. Signal too low
ECM-1826 Glow plug relay, position. Faulty signal

Symptom 1 and 2 appears to have been cured by replacing EGR and Boost pressure sensor, adjusting vacuum tube and changing fuel filter.

Symptom 3 remains.

Along with the symptoms, noted what looked like leak behind engine, below solenoid. Technicians never found what it was.

Noted by me though is that the tube running from the solenoid into the air intake appears to always be oily. Whether this is normal or not I don't know. It is a car after all.

There is no smoke, no uneven running on idle and as I said, turbo is ok.

Now, one garage have noted that the turbo wheels appear to be a bit stiff and therefore suspect that a new one is needed. However, I don't think this is relevant, based on my understanding that the turbo isn't in use < 2500 rpm.

More interesting is the possibility that there is something wrong with that solenoid tube or something near it, that the EGR is still dirty (despite being replaced) or that there is some electronics that have gone wrong (relating to ECM-1826).

I have also noted that in the manual it states that the EGR is not in use during full throttle due to safety reasons. I am quietly wondering if that is because it reduces engine power?

So, in my case, is this system not functioning properly and is that why I don't get power so that I can reach the rpms where the turbo kicks in?

Having seen a lot of posts, but few very clear answers, I am posting this in the hope that someone will recognise the symptoms so that I can steer the Volvoites here to fix the right thing.

I have one thing left to do myself, which is to reset the engine management system by removing battery overnight.