I know old post, but this sounds similer to what mine is doing. I pulled up to a stop light and it started chuggin' @ idle down to 250 - 300 rpm, I put it in neutral rev it and it went right back to chuggin'. Then I turned the defrost off and it idled up to normal. It has done this several times lately. I know because of that it had to much load @ idle. In the summer the idle would droop to 450 - 500 and i would just give a quick tap on the trottle and it would correct its self that dosent seem to be working in this case as the droop is geting worse. I have had efans for about 18 months, but there not hooked to the pcm, insted i hooked them to a temp switch.

If I hooked them to the pcm would that let the pcm be able to correct its self easier? or does it even matter. Is it sad that I own my own danm shop and between me and the three master tech we can't figure it out?