Frustrated...
Driving an 740 turbo Automatic, Bosh ignition.215,000 miles
Few months ago idle control valve started acting strange idle went up to 1600-2000 rpm for a while sporadically, then one day - permanently.
- Went to mechanic, they said that they ICV was OK but the signal from the comp. Was forcing it to stay open all the time. They claimed that they did replace the ICV with " known working one " then they replaced (or at least they said so) the computer and they said the car was OK after that but just for few minutes of driving. They told me to come back for further "investigation " - I already had $250 bill and being frustrated that they didn't fixed the problem I walked out and later I did a "shortcut" of the ICV-I put a piece from aluminum can on the way of the exit hose of the ICV with a small hole in it, in doing so to restrict the air flow.
It was summer and I was doing OK.
Two months ago I replaced new ignition wires, new spark plugs (NGK Platinum)
Just a week later I felt loosing power and symptoms of bad burning process- like running on a three cylinders every other revolution or something - then problems starting one day - took the spark plugs out ( platinum sharp-tipped ) - they were oily-black-dirty. Cleaned a set of old sparks - started right away.
Meanwhile I replaced O2 sensor, checked the temperature sensor - looks OK - reacts with different resistance on temp changes etc.
Now ( Cleveland , Ohio F 32 outside ) I couldn't start the engine. Misfiring etc.

I would appreciate any help on the issue of the ICV !!!
Also - anybody - any "issues"with regard to Platinum spark plugs and old cars ?!?!
Also what are the consequences of the " high negative pressure" in the manifold, when ICV does not work and sudden deceleration?
- I am definitely buying a new ICV, since I do not trust 100 % that particular mechanic (anymore) and maybe for a back- up (because I do not trust myself and the voltmeter) I am buying a new temp sensor too.

Thank you!