So I went back in the thread... and see you put a new TPS on it. Chances of both being bad causing the same issue is slim. But did you set the voltage on the new TPS?
Could just be spitting in the wind but I think I would reset the idle speed using this procedure from a sticky in the 2.9L forum...
So i had a surgeing, kinda low idle i was blaming on the charging system. I still think that might be an issue but i happen to run across this... I know the 2.9 is famous for its shitty idle, but i did this procedure and inital results are amazing. It idles about as good as my 97 460. Ill...
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Once idle speed is set... set the TPS voltage. I "think" the spec is .96 - .98 volts at base idle. Should also be about 4.5 volts at WOT. To check voltage on the TPS... you pierce the insulation on the TPS signal wire using a straight pin. Then use a DMM to check voltage on that circuit with key ON. To test the full sweep of the TPS... I still have an analog volt meter. I use that to watch for a smooth increase in voltage all the way up to WOT. A DMM in that case is just too jumpy to see what's really going on. This is the schematic for my 86... not sure if it's the same.
View attachment 107344
Like said... I would do this just to ensure you have the correct baseline... then you can just cross it off the list.