engine idle

So heres the deal. Start the car Idle goes high(2000rpm) then settles right away to ~1000rpm thats normal. If I let it sit without going in gear or touching the gas the idle will creep up to 2000rpm at most but ususaly around 1500rpm. When put in gear at this point it will hit it pretty hard and then the idle will come down ~200rpm. Drive away and it will run fine till at a traffic light it will idle at ~1100 and then creep up like before and it will go even higher if put in nuetral or park. Leave the light and it runs fine. At every light the same thing. Untill it has been driven for about an hour or so (not in stop and go traffic) , then it will idle at ~1000rpm ever stop as long as its less the 5min.
It has a new IAC and TPS. I have taken the throtle body off and cleaned all out. Replaced all the vacuum lines and the CCV grommet and line. Set the TPS idle voltage at 0.2V and the highest WOT setting I could attain was 3.8V at this idle setting. The MAP sensor is reading 1.8V at 1000rpm and it get lower as the rpm increases. 4.8V with no vacuum. So that looks like its fine. Unplugging the IAC when the idle is at 1000rmp will not stop it from raising(IAC macks no difference). Disconecting the MAT makes no change either. And no I've not pressure washed the engine conpartment.
I am quite confussed by all this
its a 5-90 4.0L I6 auto with ~210,000+ mi on it
Sorry for the long post but wanted to be as clear as possible. Any help would be awsome.
Thanks Fletch

When you replaced the IAC did you clean the seat inside of the tb against which the iac pintle presses when closed? If not crude could be on there keeping it from sealing closed. Quick test on your pre 91 is to disco the tb hose to the air cleaner to gain access to edge of tb above the iac. You will see the iac air intake port. Block this off while idling to see if you idle goes down. If it does so suspect a dirty iac tb seat (or pintle tip). Also your base idle at full warmup in drive should be about 700-800 not 1000.

If the idle increases as the engine warms up then check for a vacum leak at the intake manifold due to slightly loose intake manifold bolts. Tighten the center ones first and work out to the ends. Don't forget the bolts underneath the manifold. I have to tighten mine about once a yr. It makes about a 200 rpm difference sometimes.

Once all that if fine then check your base idle air intake port all the way from the top edge of the tb above the base idle adjustment screw (the one that was or still might be covered by the no tamper metal cap on drivers side of tb) to the exit inside the tb below the throttle plate). Unscrew the adjustment screw clean its tip and the port top to bottom w. tb sensor safe cleaner using some tobaco pipe cleaners. Set your base idle at full warm up w. your hand covering the iac intake air port to prevent the base idle from being affected by the iac.

These are a few things that have helped me over the yrs. Good Luck. Greg

i'll give the bolt tightening a try next time i can work on it. I have no garage and it raining a lot here lately
Any other ideas are welcome
Thanks Fletch