Thanx, Stephen, but all I can do is guess. Here's my guess.
There is no plug for the APCM on the 2000 PSD Excursions, but lots of folks with 2000 Excursions have wired in the APCM.
There won't be a plugin on the 2001 Lariat because it will have the same wiring harness as the Excursion - but there is no reason the APCM won't work if it's wired in.
So agree with your dealer to order the idle control kit for you. If he's willing to sell it to you for truck invoice price of $178, then that's a real bargain. Look in the forum for PSD Excursions and you'll find instructions on how to wire it in so it will work just like on the cheap trucks.
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Ole retired guy in west Texas with Darling Wife and Sierra Blanca - the white mountain of a '99.5 F250 diesel-powered CrewCab.