H/C Ls1 Climbs to 20.1 AFR?
 

I have a Heads/Cam T56 1998 Camaro that is tuned through black bear. The car runs great at Wot around 12.0- 12.5Afr but for some reason when its just sitting there it will climb all the way to 20.1 slowly for a few seconds or until i give it a rev, sound of the car changes too but idles right at 1k rpm like it should. Also when its warmed up and i press the clutch in coming to a stop it will give me a small power surge and drop rpm around 700. My tuner says i have a small PCV leak in the system but after numerous smoke tests/ resealing lines and putting a whole different intake on he still says he cant tune it anymore because of the leak. He said "It's not so bad as to cause a check engine light anywhere, but still a 20% correction under extreme vacuum". All gaskets are new and torqued to spec/ triple checked. New catch can that was pressure tested with the lines and ls6 valley cover,New valve covers with GM gaskets, New oil dipstick and o ring, all connections on the rear of the ls6 intake are checked and sealed. Throttle body is stock but ported.The whole engine is new with no corners cut so this is extremely frustrating at this point and not knowing much about tuning my question is, could it be a bad IAC sensor or anything else making it act like this? Has anyone ran into a similar problem?

Have you tested for exhaust leaks?

I have same issue as OP. I'm really starting to believe it is an exhaust leak that gets worse at the car warms up. This article is really eye opening. I had no idea how much something so small could affect the AFR. Just poking holes in the headers raised the AFR 7 points.

https://www.hotrod.com/articles/exha...nsor-readings/

Baseline Pull

MTX-L PLUS Reading:
Idle: 10.8
Cruise: 13.0
WOT: 12.2

Test 1: Blown-Out Collector Gasket

MTX-L PLUS Reading:
Idle: 22.4
Cruise: 20.1
WOT: 15.1

Test 2 Header Gasket Failure

MTX-L PLUS Reading:
Idle: 15.3
Cruise: 14.1
WOT: 13.2

Test 3 Poking Holes in Header Tubes

MTX-L PLUS Reading:
Idle: 17.4
Light load (cruise): 16.3
WOT: 12.5

Thanks for the information guys. I did have a couple small exhaust leaks near the band clamps on my new texas speed ORY but i had no idea something that small could effect the car so much. Im looking in the engine bay when i guess i should be looking more under the car. The car currently has a slp loudmouth to duels after the Y pipe so i think il order the rest of the texas speed exhaust kit with the cutout and try to reseal everything. Very good information.