Odd idle problem, 3.5 V6

Hi guys, I have a 99 Intrigue with the 3.5. I am always in the market to upgrade to the Aurora! Anyway, I have this posted in the Intrigue forum, but I figured I could try here too since the engines are the same.

I have searched the forums for answers, but I am not finding anything definative. I have a strange idle issue. When I start the car in the morning, it is fine. But after driving for a while, the idle slowly works its way up to about 1500 RPM. This makes it difficult in traffic as the car doesn't like to slow down without using the brakes. When this happens, the transmission starts acting wierd as well. It takes longer to upshift, as if the tranny thinks I am stepping on the gas harder than I am. Then if I add just a little power, it will downshift way before it normally would. After parking the car for several hours, when started again, it will idle anywhere between 1500 - 2000 RPM. I shut it off, start it, it does it again. But, always on the third time, it is fine. But half way home (about 25 minutes on the highway) it starts creeping up again. I don't have a lot of money and I don't want the dealer spending it all searching for the problem. Does anyone have any ideas? Again, 99, 3.5 with about 97,000 trouble free miles.

By the way, I love this engine. I am thinking of test driving a 4.0 just to see the difference! Is there a big difference?

i believe there is an "idle learn" procedure you can do.

engine hot and OFF
turn key to "run" (not start) and leave it there for 3 min
turn key to "off" for a min
restart

hope that helps

Thank you. I tried it today. Unfortunately it did not work. I went to Auto Zone. They read the codes for me, the only one was throttle position sensor. $30 and 1.5 hours later, I replaced it, and all is well so far! I am hoping it will stay that way!