Unable to Idle After Valve Cover Thread Repair

[art12321]

Hello All,
First-time poster, and a long-time reader.

I have a 1991 BMW 318i E30 (M42 engine) and have been dealing with weird startup problems since installing threaded inserts on a few valve cover threads about a week ago. The car ran just fine before besides a weird intermittent warm start issue that never really affected performance. I only installed 4 thread inserts and a new valve cover gasket. Obviously, I removed the spark plug wires to take the valve cover off, but besides that nothing. I am at my wit's end and unsure where to go from here. Below I have listed the symptoms and what I have tried.

The issue I am running into is the following:
• Cranks Fine
• Starts for a single cycle or so
• Dies along with a backfire that occurs about 70% of the time.

Video of issue: https://photos.app.goo.gl/ydNnREJ6pYXkbneR6

So, looking at this rationally, it's possible that the spark plug wires were damaged at some point during assembly or disassembly. Although, the backfire makes it a weird situation and in my head I am thinking, “This screams timing issue” but I am unable to isolate it.

Here's my thought process and what I have tried at this point:

• I only messed with the valve cover gasket and threads, in order to do that I removed the spark plug cables.
  • Perhaps I broke something there. Replaced spark plugs, tried alternative plug wires, tried coil on plug replacement (cheaper than new coils or new plug wires)
  • Checked for spark on current wires and new coil on plug setup, sparking fine.
  • No Change [-1 spark issue]
• My friend thought it was a firing order issue
  • We attempted an “alternative” wire order (1234 -> 4123). Believe it or not it started but ran roughly and needed constant throttle to keep alive. Hindsight this was dumb but gave me useful data.
  • During this attempt, the car threw lambda 1 code, replaced O2 sensor.
  • No change. [+1 timing issue, -fuel -air -spark -O2]
• New spark plugs
  • Checked for gaps and fouling. Noticing they were wet with gas.
  • No Change [-1 fuel issue]
• Ok perhaps a chip from the threads caused a valve to stay open or something.
  • Compression test was done, 180psi all around.
  • Opened the valve cover again to see if anything was off. Visual inspected No signs of issue. The timing chain seemed fine, no signs of marring on the chain protector, The timing chain tensioner changed a few years ago.
  • Checked the seal on valve cover gasket, made sure the mating surface was clean. Removed old gasket material with plastic razor blade.
  • Did notice paint pen on chain and cam sprockets, perhaps a timing change occurred? Has been otherwise running fine, but interesting?
  • No Change [+1 Timing?]
• Camshaft or crankshaft position sensor damaged somehow?
  • The resistance reading normal on both.
  • The current crankshaft sensor has a crack in the wire casing.
  • New aftermarket sensors were ordered and installed, no change. The replacement crank sensor wire is too short for whatever reason.
  • A spare crank sensor from a parted car was attempted but the same issue persisted. (unknown functionality of this sensor but came from an m42 with blown head)
  • Interestingly I found that if the crank sensor was rotated to different angles, the car would start but run rough similar to the alternative spark plug wire order.
  • This was hopeful but I believe this is due to the sensor detecting TDC incorrectly and essentially acting like it would with different spark plug wire order.
  • Video of this happening: https://photos.app.goo.gl/3V14oA5nDqSCy4DJ9
  • No change [+1 timing issue]
• Vacuum issue or air issue?
  • This is difficult to test for without a running engine.
  • ICV checked visually for fouling and functionally using bench power supply
  • Vacuum lines visually inspected for cracks; this has been an issue in the past. I have changed a ton of these hoses in the past because of this. (“Mess under intake”)
  • Tried another MAF (from same part out car, unknown functionally).
  • No change.
• Fuel?
  • My fuel pump started the hum of death a few weeks before this issue. I had sourced a replacement ahead of this issue occurring. This was changed just in case since the issue began.
  • No change [-fuel]

To recap I have done the following:

• Stock coils and wires were checked with sparkplugs grounded to the frame.
• The coil on plug setup was checked with sparkplugs grounded to the frame.
• valve cover gasket (circumference gasket) changed
• Valve cover spark plug gasket seals were visually inspected and cleaned.
• Valve cover bolt seals were inspected and cleaned.
• Replaced spark plugs
• Swapped to coil on plug to make sure it wasn't coils and wires
• Battery wire fuse checked
• Coil wires checked if installed correctly via ECU.
• Camshaft position sensor tested with new aftermarket sensor
• The crankshaft position sensor tested with new aftermarket sensor and spare OEM sensor
• O2 sensor changed
• Spare MAF sensor tested
• The fuel pump was going out before this issue began, swapped in a new fuel pump
• Turner performance chip was installed before, this was swapped back to OEM.

I am at the end of my rope and unsure where to go from here. This is my daily, and I love this thing. This is the first time I have been genuinely stumped. Any advice would be greatly appreciated. I am willing to try anything and give any additional information! I want to cross-post to M42club.com, but I am unable to make an account for some reason.

Mods, please let me know if this needs to be posted elsewhere.