The 20V that followed me home, a few problems

[TWFAUST at aol.com]

A month or two ago, I was followed home by a '91 90 20VQ. It has been hanging 
out under my barn while I replaced the rear diff bushing and some fuel lines. 
I don't have a Bentley yet (I prefer Haynes because the index is more 
complete), but I have a few problems 

Whistling noise 
There is a noise under the hood which I can only describe as a whistle. I 
can't seem to locate it. I notice the alternator belt is loose, but I have never 
heard a belt whistle. 

Slow return to idle 

If I run it up to 3000, it very slowly returns to about 2000 where it will 
hang for about a minute. Then it will suddenly drop to 1400 and then slowly drop 
to about 1000. 

Diesels 

When I shut it off today it ran on at about 600 rpm. It quit when I stepped 
on the gas (just like the carburetor days) I had 89 octane with a heavy dose of 
Techron in it. 

Does the 20V have the dreaded "ISV"? 

I notice that if I pop the oil fill, there is no difference in idle. Vacuum 
leak?

Tom Faust