I am having a similar issue. I just cleaned out my throttle body and cleaned my MAF and adjusted my idle. (Disco 97)it now idles great just below 800ish. However when in park it jumps to 2000. I will try the unplug and shut down.
Any pictures of the location of the coolant sensor would be much appreciated.

On the 97 find the upper radiator hose. Foillow to engine. To your right are two sensors standing tall from the intake. The one with square top is monitored by the ECU. The one with a single wire is the one that drives the heat gauge. On my scanner, if the square one is unplugged I show -40F for coolant temp.

When I first got "Frankensein" (brought to life with parts froim the dead ones) it did the 2000 rpm idle. Only way I fixed it was to swap ECU and IACV from a donor truck (which can have other issues). It could be that the ECU needs to have adptive values reset. These are stored memory setting that adjust to minor changes in the various components. But then it doesn't know about the repairs you did.

Ok great. I will attempt that switch out. I switched out the ECU when I first bought the truck in 2004 so I'm familiar with the process. I'm changing out spark plugs this weekend. Ordered the original champions from Atlantic British yesterday along with a fuel pressure switch.

I took the truck out in traffic yesterday and it stalled at a light due to low idle. I had backed the idle down on the thread a few turns. So I'm trying to find a happy medium. Stupid question: do you recommend manually adjusting idle

Thanks for your very helpful responses also what kind of wires do you run in Frankenstein?

It is important to note that I can idle below 2000 in park but it's too low, maybe 550? So it begs the question is it the fix you recommended or if I do the swap out of the IAC and ECU will it give it a truer idle below 1000. Thanks!

PPS I am also experiencing a good amount of engine hesitation from time to time. I just had a new fuel pump from AB dropped in and changed the fuel filter so I can rule those out. I attempted a 2/3 seafoam last night. I put half a bottle in the gas tank (filled to ab 2/3 of gas) and put the other half in my oil crank case. I drove for about an hour and didn't experience any "white smoke" coming out of the tail pipe. I held back from "seafoaming" the vaccum hose because I don't have any experience doing that 1/3. The truck was sitting for 2 years in a storage space so I am doing my best to get it back operational. Aside from the high idle (which is a recent development due to manually adjusting the idle by hand because it was idling around 550 and stalled yesterday)and time to time engine hesitation it is running pretty well. I also did a throttle body and MAF job on it last weekend. Full disclosure


QUOTE=Savannah Buzz;423780]On the 97 find the upper radiator hose. Foillow to engine. To your right are two sensors standing tall from the intake. The one with square top is monitored by the ECU. The one with a single wire is the one that drives the heat gauge. On my scanner, if the square one is unplugged I show -40F for coolant temp.

When I first got "Frankensein" (brought to life with parts froim the dead ones) it did the 2000 rpm idle. Only way I fixed it was to swap ECU and IACV from a donor truck (which can have other issues). It could be that the ECU needs to have adptive values reset. These are stored memory setting that adjust to minor changes in the various components. But then it doesn't know about the repairs you did.[/QUOTE]

Update:

I replaced the spark plugs with champion copper that AB reccomended. I also cleaned the iac with throttle body cleaner and attempted to clean the TPS but just was able to pull the back off and nothing looked like it needed it. Also cleaned out the connection on the throttle body that holds a tube that goes from the crank case to the throttle body. It was really gummed up. Cleaned with throttle body and used q tips to remove buildup. Took my wife to work this morning and it ran pretty smoothly. No hesitation. I'm going to spare digging into the ECU for now but the next step for me includes swapping out the wires now that I've covered the plugs with STI wires and throwing in a Fram or K&N air filter.