20v RPM's not dropping

[Brooks Ellis <brooks@fortnet.org>]

        I was driving a '90 20v Coupe Q the other day, and I noticed that
when I took my foot off the gas and hit the clutch at the same time, that
the RPM's would not drop right away. They would stay at the same frequency
for about a second, and then drop. 
        I have driven other 20v coupes and they did not have this problem,
nor does my 10v.. 

        It seems that I have heard of this happening to other list members,
but do not fully recall the exact nature of the problem. A sticky throttle?
Idle stabilizer...?
        
        If you could tell me, and how much it would probably take to fix it,
I would really appriciate it...A 20v coupe sound great compared to my 10v
sedan; but if I am going to have to put some serious $$$ into it, forget it.

Thanks a lot!!

brooks