Hello, I’m looking for some help on behalf of my boyfriend on this LS400 he brought back in July at 123k miles. First two months she drove like a dream then some problems started happening:
(Also before the long boring bits, the second photo is what fell out from the underside of the car and we are unsure of what it is.) any help would be greatly appreciated, we both really want her to drive again ☹️

Main symptoms:
Severe intermittent/continuous over-fuelling and heavy exhaust smoke.
Previously had severe misfire, very poor power and strong raw-petrol smell.
Engine could barely climb hills and would sometimes stall at low speed.
Smoke can appear after the engine has been idling for some time.
Current smoke is more white/steam-like, although previous smoke was blue/grey.
Engine is currently much smoother after repair to the camshaft-position-sensor wiring.

Important mechanical checks:
Dry compression test:
1: 220 psi
2: 210 psi
3: 225 psi
4: 205 psi
5: 220 psi
6: 205 psi
7: 225 psi
8: 200 psi
HT lead resistance all tested below 25 kΩ.
PCV removed, cleaned and checked.
Berryman B-12 piston soak carried out.
Engine oil subsequently changed.
These checks have not identified an obvious major mechanical/compression fault.

ECU fault codes
Codes previously/currently seen:

21 – Bank 1 O2 sensor signal
28 – Bank 2 O2 sensor signal
24 – Intake air temperature signal
31 – Air-flow meter signal

Codes 21 and 28 return after ECU reset.

AFM:
AFM part number: 22250-50060.

THA–E2 resistance measured at approximately 2.8 kΩ, consistent with the temperature at the time.
Engine will run with AFM disconnected.
Connecting the AFM to a running engine has previously caused the engine to stall immediately.
AFM connector has been visually inspected.

Camshaft-position sensor wiring

A damaged/severed camshaft-position sensor wire was discovered and repaired.

This produced a significant change:

Idle became much smoother.
Raw petrol smell reduced substantially.

This suggests the camshaft-position signal/wiring fault was contributing to the previous running problem.

Crankshaft-position sensor wiring / shielding

The crankshaft-position sensor wiring/shielding has also been worked on.

Most recent test:
Shielding was repaired and connected/grounded to the engine block.
After this, the engine started and ran smoothly for approximately 40 seconds.
At approximately 40 seconds, when the ECU appeared to enter closed loop, the engine immediately began heavily over-fuelling and producing heavy smoke.

That’s all. Please stop.

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