I bought a 2.0 TS 147 with a blown engine, and popped another engine in with little drama.
However, error code P0505 idle control popped up regularly and sure enough, it didn't idle steadily.
Lately P1173 and P1176 (mixture lean) started popping up as well.
I found that the red 50mm O ring between the throttle body and plastic inlet plenum had done a Lord Lucan and just vanished! That's where the air was leaking in!
As I had bought the replacement engine without the throttle body I guess it had been lost before I got it, but inexperience meant I didn't spot it absent at the time. I've since done a 1.6 - 2.0 transplant (which have different plastic plenums) and so noticed it immediately when investigating the fault today