Throttle body failure or not??

[sfcl]

Hi all,
I described my problem on this forum some days ago (thanks again Waesel!) as a probable throttle body failure as my Peake scanner displayed more and more often the code 88 (table 19) so a "Throttle position sensor, adaptation selftest". I finally showed the car to the local BMW agent (remember, I'm in the islands so no big BMW dealer here...) and he says that he doubt that it is the cause of the failure and he suggest to let the car so he can check. I'm quite confused now!
Giving that I wouldn't like to pay hundreds bucks for just a check, still without knowing exactly where is the problem I guess, maybe you can help me a bit more?

The problem: It occurs only at very low engine rpm, means when the engine is at idle speed or when the throttle pedal is very slightly pushed.

- If it is at idle, the engine runs well for some minutes then begins to misfire and finally stalls. The check engine soon light comes on when the misfires occur. Ther EML light and limp mode don't occur all the time, sometimes yes, sometimes not.

- If it is at low throttle openings, the engine speed varies, means it passes from (for example) 1200 to 1500, then 1200, then 1500 all the time every second (means the engine speed varies - pulses- by about 300 or 400 rpm ebvery second or so). Then the check engine light somes on, and sometimes only the EML light and limp mode.
Most of the time however, the limp mode and EML light only occur when I restart the engine after a stop.

If I run the engine at high engine speed (above 2000 rpm) so most of the time on open roads, there is absolutely no problem, the engine runs fine and strong. This means that the problem occurs only if the engine idles or at very low speed, so only in trafic or in town.

Noticed that sometimes I get 2 codes with the Peake scanner: 88 (Throttle position sensor, adaptation selftest) and 73 (Throttle position sensor, adaptation).

What do you think? Does you think that the throttle body in the only cause (I would have thought that a failure in the throttle body would affect the whole range and not only the low speeds)?
Thanks in advance for you help!