cold idle creap and terrible (fatal?) noise

[eddiec]

i finally have my 91 240 running again. but its cold outside and it wants to idle very high for quite a while (like 5-6 min).

from the top heres how it acts: after starting i let it run for about 6 minutes before touching the gas. it was idling @about 2-2.5k (and the temp gauge had not budged), i gave some throttle to about 3k and held that for 10-15 sec. then gave more throttle to about 3.5k and held. did this in .5k increments holding breifly to about 5k. i then let off and the idle came down to about 800 or so. the temp gauge registered about 2 lines worth (whatever that is). then the idle crept up to over 1k and it looked as if the temp gauge dropped a little as well. i know this problem is minor to whats next but maybe someone has had this problem.

also a get a nasty sound (maybe from under the valve cover) at about 3k upto about 4k and it stops even as the revs continue up. when i let off the gas from above 4k it makes the sound, as the revs drop, throught the 4-3k rpm range. as a note the exhaust manifold heat sheild has been removed as i thought this was contributing to the noise, kinda of a resonance actually.