Hi. I am old school (points, carburetors era) and am really baffled. I have a 93 E350 van with a 351 W. The exhaust was leaking, so I took it off for repair. The 2 tubes running to the cat converter were rotted off, not connected. It ran fine, just loud. I welded the holes shut in the converter and rerouted the 2 lines into each other. Still ran fine. Then I changed transmission fluid and filter and replaced the radiator. Now, the check engine light is on, idles real fast, shifts real hard, runs rough. I checked for vacuum leaks, rechecked the timing. I unhooked the throttle cable at the engine to make sure it wasn't sticking. Can't find anything. I finally unplugged the connection near the throttle cable area...and it idled down, but now starts hard, check engine light still on, still shifts hard. There is a coolant sensor somewhere,,,with me draining and refilling the antifreeze, could this sensor "stick"? I have ran it and driven it enough to where I am certain there isn't air in the system, runs cool, heater works great. I was told that if I unplug that throttle sensor thing and it idles down, that that sensor is bad. But isn't that sensor being told to speed it up, because of something else wrong? I am really stumped. Any help really appreciated.

 

It sounds like the Idle Air Control (IAC) is what you unplugged. It could be the IAC is clogged or needs a cleaning. Your right its not a sensor but an actuator and it could be getting a signal to open. Pull the codes and see what the computer is saying. A temp sensor or the TPS could be the issue.
Regards
rikard