Thanks for that - but I'm still no further forward.
P0238 keeps coming up. Likes to come on between 2500 and 3000 rpm when I'm booting it.
** Disconnecting the VGT solenoid vac pipe to the turbo yields no boost (both when driving the car, and on FIAT ECUScan when tested stationary - stays at around 1000mBar)
** The MAP sensor gives reasonable values - at idle it reads atmospheric, and during driving the readings go up (and when the MCSF light comes on, are around 2800-2900 mBar). I have cleaned the sensor - no benefit.
** I have stripped and cleaned the VGT solenoid, and when tested in ECUScan it appears to be working
** I have cleaned the electrical connections to the MAP and VGT solenoid, including the multiplug that sits just in front of the battery
None of this has made any difference.
I've had a run with FIAT ECUScan connected. The VGT solenoid opening starts at 75% (at idle) but only goes as low as about 53% at higher revs. I assume this figure is the ECU "command" to the VGT solenoid as there are no 'feedback' sensors on the VGT solenoid to tell me what the "actual response" to the ECU command is.
While all this is going on, at idle, Desired boost and Actual boost are the same. As the revs rise, Actual boost starts to part from Desired boost, such that by aabout 3000 rpm the Actual boost is some 800mBar higher than desired. This seems to be what is triggering the MCSF warning light.
My question is this... is there anyone out there with a 20V JTDm who has had exactly the same problem and has successfully fixed it (both on the road, and on Fiat ECUScan graphing). I don't want to just start buying components in the hope they will work. It seems to me that: turbo is OK (with no vac, it produces minimal boost, as it should, so vanes not stuck), MAP OK (reads atmospheric OK and varies smartly with changes in engine speed - can these fail by "reading high"? - anyone know?), VGT solenoid - seems to be moving OK (but is it moving enough? - are the seals leaking a bit? - I don't know).
Anyone out there with a 20V that's been hooked up - what sort of readings do you get on a 'healthy' car?
Thanks for reading chaps/chapesses!