fast idle on 5.0 '88 chev

[gwbar]

I have a very good '88 caprice with 180,000 miles but runs and drives like new. The only problem is that it stays on fast idle for a very long time and when shut down it diesels.
I ran the car for about 30,000 miles with the choke wired open so it would not idle fast but I'm giving the car to my daughter and I put it back to normal operation and once again it idles fast as in the past but starts easy again.
Does anyone have any suggestions?
gwbar

[Luke@tirerack]

Sounds like the timing issue to me .... advanced timing would cause your problem ... another issue you might want to check in an intake leak commonly seen at the bottom of the throttle body/carb.

[James Bond 007]

Try To Replace the Idle Air controll valve or the Throttle body is worn and is drawing in air through Pivot (rod) or one of the Intake ports is plugged with corbon you wont be able to see that unlees you take the intake off.