This started a few days after I replaced battery. Code P0506. Truck drove fine,no low idle problems observed. Read where this code can come up after battery change. Cleared code, a couple days later check engine light back on. Figured it was same code so drove it for few days with no problem. Went to clear it again, but this time the code was for p0128. The heat works fine in truck, I have noticed the temp gauge stays a little under half way. Truck still appeared to he running fine. Cleared that code. A day later check engine light back on. I check it again and the p0506 code shows up. What could be causing this? Like I said truck is running fine.

 

I would replace the thermostat and clean the throttle body.