are you throwing some codes ?
check engine light going off for a little bit .
i slipped into running very rich a few months ago , it turned out to be vsv switches located under the intake one is for egr and the other for fuel . they are easy to test but hard to get to . you'll see under the intake a mess of small black hoses going to and from two brown and black little things about 2.5 inches or so
see here:
http://www.cygnusx1.net/supra/librar...10/1708_3.html
part# 25860 and 17650 the EGR is # 25860 just check for continuity . zero = toast .
i use an air/fuel gauge so it's very easy to spot variances in the mixure from screwing around with mods .
i am not saying this is your problem it's just another option to try .
another option is to adjust the base idle screw
what does it idle at now ?