Hey Scotty, I got a question about my 1999 Silverado 1500 with the 5.3L engine and 357,000 miles. For a couple of years now, I've had a high idle issue. I will start the truck (it will not act up upon start up) and I'll drive for a bit, or sometimes just a few feet, then shift it back into park and it idles high. The idle will reset itself once i turn the truck for a few seconds, then turn it back on. I have also had a high idle surging, about 5 times throughout the 2 years, where I'll put it back into park, and it surges from about 300 - 1000 rpms back and forth.
Other info: I have replaced the IAC valve on the throttle body, and that has seemed to help, but the issue still persists. The issue only happens in the winter time when it is below 40 degrees. The truck will also shift at higher rpm's when the issue occurs. Everything else on my engine is original and no codes are being thrown.
However, during a recent cold snap, it got to below 0 temps for 3 days. During that time, I did have lean codes on both banks, and a pending code for the MAF sensor, but that went away as soon as we got above 0. Please help!! I have no idea which way to address this!
Start off by cleaning the MAF sensor. When you replaced the IAC valve, did you inspect the rest of the throttle body? If not, I would also clean the throttle body while you're at it.
I didn't inspect the entirety of the throttle body, but from everything I could see, the throttle body was clean. I do have throttle body cleaner though and I most likely will clean it anyways. And ok, I will clean the MAF sensor too.