Need some help
I’m chasing a problem with my 5.3 swapped s10.
It’s a 2002 LM7 with no cats, only upstream O2, no egr.
The truck runs very rich, my obd2 reader shows fuel trims up around 25% while idling in my garage at operating temp and I can’t seem to figure out why. My best guess is a vacuum leak somewhere, but I’ve never been able to find one. The only other thing hinting at a vacuum leak is a high rpm start when cold (2000rpm) but then idles down within 5 seconds of starting and seems to run perfectly fine after that.
No check engine codes except for a knock sensor code that popped up this week. The high idle start has been happening as long as the engine has been in the truck.
Any ideas for other things I could check?

