How’s it going? I’m new to the whole forum thing, along with diagnosing and fixing vehicles. I got a 2002 Deville roughly 5 months ago. It has the 4.6 and only had 94,000 miles. Car fax says it had only one owner and it was registered under a business. Not to mention it showed it being serviced frequently.
Car ran great all winter no issues at all. It is now up to 105,000. It started to rev high while in park and while driving. In park it was around 800 rpm and while driving it would be around 1,200 rpm sitting at a red light. I got lucky and the engine light came on one weekend I was able to get to autozone. It had been only coming on in the mornings going to work. The said it was reading a high idle and said the issue was the IAC valve. Part was 220$. I ended up getting throttle body cleaner, cleaned the valve and nothing changed. I heard a vacuum leak and located it with the TB cleaner. The boot connecting the air intake had a leak. I managed to change it out with the help of YouTube and several calls to dad. Car worked great for about 3 weeks. Started doing the same idling issues and I figured out how to get the codes off the dash. It reads ITC U1016 history and PCM P0507 current. I cleared it after all the work I had done. I believe the pcm is the high rev code. Any thoughts? I appreciate your time!

i only get 16.7 mpg on the highway recently also