Aloha all; I transplanted an '02 LS1 into my '97 Miata. Motor ran fine previous to transplant. New harness from Chevy Thunder, cats deleted, and cpu reprogrammed to reflect changes. Ran rich on drivers side with black plugs even though I had only driven it a couple of miles on original plugs. Right side plugs looked good. I changed O2 sensor on left side as there was no signal to mechanics computer program. I changed plugs with NGK/Tr55 gapped @.045 per mechanics directive. Runs even worse as it idles roughly and runs as if it is only running on 4 cyls. Stalled out at stop and hard to start again although it did and continued to run roughly until I shut it down. I have not had an opportunity to have it on a computer post plug and O2 changes.
Suggestions as what to do to rectify situation? TIA.

 

You'll have better luck and a greater tech base on LS1Tech.com (Specifically their conversions/LS Swap Forum). What are the mods to the engine? What ECM are you using, etc etc.