What year is the car?

I suggest your AMM is on the way out. Mine did the same thing with a repeating code 2-3-1 for around 3-4 months, then the AMM caused an inability to drive.

Swapped out with a good used one, no problems since then (1 year ago). No error codes.

You might want to try a couple other things:
- Clean AMM connector and apply a tiny bit of di-electric grease;
- Pull off vacuum hose from fpr, see if any fuel in there, if there is replace fpr (unlikely since you do not complain of drivability issues)
- engine temp sensor connection or malfunction of sensor? (check FAQ like 700)

Otherwise stock up on a good replacement AMM, abundance on ebay, but make SURE you match the last htee digits (i.e. 007 or 016 or other). Avoid "rebuilds".

Greg Mustang
Montreal - Ottawa
Canada