I had a P1687 the other day. "Metering oil pump" = the throttle valve really.
As you can guess, it means the ECU is having trouble understanding the feedback from the TPS (the throttle position sensors) so it will go into limp mode to safeguard the engine. In my case, it was the aircon linear pressure switch which is fed from the same 5v supply, (my fault as I was playing with the air con at the time). Mine was easy to sort out but it shows that a problem on the linear pressure switch can throw out the throttle body circuit too
Anyway, the system is like this
The ECM is your ECU
Your throttle body has two resistance pots or tracks inside which provide feedback voltage to the ECU to tell it where it is. They're different voltage ranges so it can very accurately determine just where the throttle valve is.
Throttle valve motor and pots
See the two potentiometers here? That's what your ECU is having trouble with.
The outputs from these pots look something like this
This isn't a Stilo but it shows the different voltage feedbacks as a throttle is opened and closed
If someone has a scope then you can trace the feedback voltages from the throttle position pots and see if it's a clean and smooth feedback thoughout the full throttle range with no sudden jumps or spikes
Ok Nodding off yet?
Now a bad contact here at the throttle body connector would cause your problems so I'd use some contact cleaner (NOT WD40 but proper electrical contact cleaner) on the connector
Then I'd get up the other end at the ECU and recheck the connections and some more cleaner there to freshen up the contacts and, of course, check the ECU earths
Again, someone with a scope could check the output voltage from the ECU and what's actually feeding back to the ECU from the TPSs before condemning the ECU. It could well be the ECU that has a problem but it can only go on the information it's given from the throttle body