high idle help needed

[jos1 at cornell.edu]

Folks,

My '89 100Q at 226K miles has suffered from a high idle/rich running 
condition for some time now, in spite of having had the ICV replaced 
twice, and the O2 sensor once. I notice that constricting the air flow 
to the ICV by clamping the hose does help somewhat, but by the same 
token removing the oil dipstick or even the oil filler cap does not 
alter engine speed.  From having read posts in this group I'm guessing 
there must be a vac leak somewhere (?), but as a non-mechanic type I 
need to learn what to check, preferably with a road map of where items 
to be checked are located.

Can anyone point me to an appropriate source please? I've not had much 
luck browsing the archives.

Thanks in advance for any assistance.

JOS