Crankshaft position sensor problem


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Mar 15, 2021
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2011 gmc terrain 2.4 120k miles.
So vehicle ran good till it didn't. The timing chain skipped. Long story short, took it into a reputable shop. Had new chains, piston rings and ect installed. HOWEVER. The crankshaft position sensor was missed. It happens, I work on large trucks and it happens. Here is were things get wierd.
The the crankshaft sensor UNPLUGGED.
The vehicle will start after a few seconds. Runs great, no tachometer, stabilitrak light comes on, and it throws a check engine light. But it will stay running.

With the sensor PLUGGED IN
All warning light go out, tachometer works, car starts right up BUT idles rough and dies after a few seconds.
Took it back. We did all the relearn procedures possible for the vehicle. It fixed it or so we thought. We cycled the engine a few times, and everything went great. Until after the 5th start up, where it resorted back to the original behavior.
Cables good, all other sensors good, grounds are good. We replaced the sensor twice in the off chance that I bought a bad sensor.
Short of a humm from the ecm everything else is checking out. GMC is even stumped on this one. Has anyone experienced this before??