I have a LS1 from a 2000 Corvette in my 1972 Cutlass. It's stock internals, other than a cam and valve springs. I have 2 issues and not sure if they are related. Since I did my swap in 2013, I will occasionally get a P1518 code after trying to start the vehicle on the next ignition cycle. It will start and stall and then just crank unless I can hold the throttle pedal down. I've soldered in 2 new communication circuits, power wire and ground wire, to my TAC module. No change. I've replaced my crank sensor 2 years ago thinking that's why it would crank so long and not start when it would get to a point where it would just crank and not even try to start, but that didn't change anything. I checked for a voltage drop and found a relay that was powering my fuse block, had a 10.4 v voltage drop on due to a weak switch side power. I connected the fuse block directly to a switch so the TAC module now has good voltage. I went to try and do a Crankshaft Variation Learn with HP Tuners, a Tech 2 and a Matco Scanner, and neither ran the test. Usually the fuel shut off is around 4200 rpm but I just put it to the floor and bounced it off the Rev limiter twice when using the Tech 2. I sat there thinking about trying to think of things to monitor for voltage and cranking or changing a tune to try and add more fuel on start up, and I started to hear a ting in my muffler. It started to happen a little more every 20 or 30 seconds it would pop. I was watching my AFR gauge and it would go 14.6, 14.9, 15.3, 15.8, 16.3, and then pop. Was talking with a buddy about it and he was messaging his friend who said I should pay more attention to the code and the engine is probably fine. I don't think the engine is that hurt (but needs a rebuild). The vacuum is about 14 to 15 in hg at idle. Sprayed around the intake with Carb clean and nothing changed. O2 sensors looked to be reading ok. Short term and long term fuel trims were all in the low single digits which says I'm not real lean. Fuel pressure regulator is at 58 psi. I monitored the communication circuits and they are displaying similar patterns within 0v to approx 5.6v. Patterns are about the same with the car on and when the engine is running. Not sure what a typical pattern from the TAC module is supposed to look like.

What other data can I monitor with either HP Tuners or a scan tool or what tests can I preform to figure out why it is popping. Am I right that the TAC issue isn't now causing the issue after 12 years. I think I'm going to do a compression test and a leak down test, just to check the internal health of the engine. Spark plugs are 3 years old I think and maybe have under 1000 miles, but I will check those too.

Videos of Noise and Test
Lean Pop at Idle.mov
CutLS TAC Circuit Testing.mov