Had the same problem with my 2.6. Turned out that the throttle position switch was not sending the idle signal. The fix was to partially disassemble the throttle linkage (the ball and socket joints down low), clean, lubricate, and adjust. The TPS is located under the fuel distributor at the end of the throttle shaft. It has three leads - idle signal, WOT signal, and ground and has a pigtail with a connector in the harness channel that runs transversely across the top of the manifold, so it is easy to disconnect and check for continuity of the correct pair at WOT and idle.
Also check that the microswitch on the top of the manifold sends the proper idle signal.