Erratic OBD codes

[Clifford Pope]

1992 240, LH 2.4, LPG conversion with mixer.

I think I have now mastered the various vaporiser adjustments, and have got the car running well on gas and petrol. Idling is reasonably smooth even on gas, and seems to "catch" reliably when pulling up.

So I cleared all the old OBD codes, and out of interest checked again after a run. It showed;

1:3:3 = No signal from Throttle Position Switch
1:2:1 = No signal from Air Mass Meter
1:1:3 = = No signal from fuel injectors

I cleared the codes, and after the next run read them again:

2:3:1 = System compensating for rich, or weak, mixture
1:1:3 = No signal from fuel injectors

After again clearing and rechecking:

2:3:2 = Compensating for rich, or weak, mixture
1:1:3 = No signal from injectors.

These seem to be completlely erratic. Obviously the fuel injectors are working, because the engine runs well on petrol and idles evenly.
I cleaned and re-adjusted the throttle body and stop, and checked the switch was clicking at the right point and giving the correct electrical readings at the contacts.
The plugs look perfect - no evidence of rich or weak mixture, and the earlier AMM "fault" appears to have corrected itself.

So is all this merely confirming the statement that the engine light always comes on with LPG, and is meaningless, or is does it indicate some underlying fault?