97 F150 idle issue

Hello! Ive got a 1997 F150 4.2 2wd standard pick up and Im having an issue with the idle? When im driving and Im coming up to a stop sign Ill put it into neutral let off the clutch but instead of the Rpm dropping to idle it seems to climb up to 1500-2000 but when the truck comes to a complete stop the rpm drops back down to idle. its had this issue for years but not to this extent. Ive cleaned the map sensor, the flow sensor, and cleaned out the idle air control valve. ive also replaced the throttle pos sensor. Im out of ideas... any help is appreciated! Cheers

The EGR (Exhaust Gas Recovery) system on that engine wasn't the best design. After the EGR valve it doesn't just dump into the main intake like most other engines. It goes into its own tubes and channels in the intake to each cylinder intake opening. These will clog up starting with those closest to the valve and eventually forcing all the exhaust to one cylinder, usually 5 and 6 (back two on drivers side). Besides making it run at very unusual high or low rpm's, it can clog up the intake and spark plugs on the remaining one or two cylinders that are getting all the exhaust gas. Pull your 5 and 6 spark plugs and see if they have a brown buildup to indicate this issue. If so, there are links to youtube videos in this forum if you search for them showing how to remove the upper portion of the intake and clean out the tubes in the lower portion using small picks and screwdrivers then vacuuming out the debris.
Eventually if the spark plugs get enough coating you will get a misfire code.
Your problem could be many other things. I've had vacuum lines with cracks under the bends that would only open with the force of deceleration and be a pain to find.
Since you didn't mention it, I assume with all you've done that there wasn't a code. But I do suggest checking that the CEL comes on when you first move the key to on position. The light does sometimes burn out, or a PO or dealer will take a bulb and spark one across higher voltage to burn it out and pop it into the dash. So I usually hook up a reader anyway, just to check.

ok so today i pulled out a scan tool and checked to see whats going on
Ive got:
P1121 throttle pos inconsistent with maf
P1000 on board diagnostic ii moniter/ drive cycle test not complete
P1125 throttle position sensor circut intermittent
the truck doesnt have cats on it but the sensors are still hooked up (should i just unhook the sensors?) so there are a bunch of codes i didnt write down before clearing the codes so i know they will be back tomorrow

just for fun i unplugged the IAC valve and it resolved the issue but id rather fix the issue then do a hack job.

Our vehicles around here have to be emission tested to get the license plates, so I don't have the experience on what to do for a vehicle without that junk. You said earlier you cleaned out the IAC. You didn't say how, when I do it I use spray carb cleaner and an old toothbrush. Making sure I get the piston super clean and it is no longer gummed up so that it will move freely. You might do the same, just saying how I do it.
Hopefully someone else can tell you how to get around it, or try going to this other F-150 forum.
http://www.f150forum.com/f6/