The truck is a 90 F250 4wd with a 5.0. The temp sensor wasn't reading right on the instrument cluster, so I replaced the coolant temp sensor yesterday. I also noticed that one of the wires for the O2 sensor was disconnected by the plug, so I reconnected it. Before all of this I was having a problem with the truck idling high randomly. It wouldn't happen all of the time but at least once a day it would either rev up to about 2k and stay there or rev up to 3500 and stay there. Now it is still doing that, but it is now reving up to about 2k then immediately down then back up and so on. I am completely lost on what this could be. My coolant temp still reads incorrect on the instrument cluster as well. Any help would be appreciated.

Edit: Almost forgot, but yesterday when I pulled into the driveway it was sticking at 2k rpm. I turned the truck off. I tried to restart it, just to see if it would run normally, and it wouldnt fire. It was acting as if the battery was dead. I checked the voltage to the battery yesterday and both the battery and the alternator are all good. My battery voltage guage actually reads high all of the time. About the 3/4 mark on the guage.

 

You replaced the wrong item, the coolant temp sensor (ECT) is for the computer and not the gauge.
You need to replace the engine temp sender that has only one wire on it.
The one you replaced has two wires.



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