sorry the 86 is actually a 17 and a 15 so codes are 12 37 33 17 15 and 55. from what I saw some make sense. Truck always has run cold barely moving heat gauge up since I've owned it(about 8 years)so code 17 makes sense and since it was fine for so many years I don't see this is the issue. Code 37 is interesting because I have a clunk from time to time I suspected was torque converter related. When I got it inspected they said it was internal issue but as my fluid is not burnt and extremely clean and shifts perfectly I had ignored it.
This still does not explain the wandering idle in cooler temps. 33 has me perplexed as this is non ac truck. No idea what code 15 could mean as I have no idea what a distance sensor is (VSS).