Decided to start a new thread because I have new symptoms that I just don't understand. I need professional help (in more than one way )

I had posted previously about my partial success in cleaning my Mass Air Sensor. Now, not so sure that it is the cleaning that "cured" the problem.

On one day, I reset the CE light and drove the car about 50km - by that time all monitors on my OBD II reader had gone solid indicating that all diagnostics had been completed - no pending DTC,s after a dozen or so short trips.

Next day, I attach the Code Reader before setting out and immediately I get a CE light! No pending codes before hand - just the DTC,s (P0170 and P0173). Thought it just may be a glitch of the meter, so reset and went for drive - in very short distance ( 3 km) CE ligbt comes back on. Next time, I repeat the process, make several short stop start trips (~10 km) and NO CE light. Next time, CE light is back on.... and so on.

Other Background:
- I have checked vacuum and it is steady at 20" HG - no apparent leaks.
- OBD meter says that O2 sensor checks have completed, presumably with no problem.
- Same for other monitors (other than Misfire, Fuel system and CC which run continuously)
- New spark plugs installed
- New air filter installed
- Previously when I had this problem, I cleaned MAS and problem disappeared for about 3 months.
- Voltage to MAS is 5.02v and resistance of MAS at 8 deg C is 4060 ohms.
- the engine runs well with no hesitation or misfire.

Given this background, is there something other than the MAS that could be causing this inconsistent behaviour? Perhaps an over rich mixture at start-up that does not happen every time?

I do plan to buy a new MAS but am not convinced that it wil solve problem

Sorry for long post and repeating infpo posted in other thread.