1998 Mazda 626 Mazda 626 RPM misbehaves + smell

The new PCM arrived, it will be installed next week or the week after.

The mechanic who does the job is quite far away, so Is there some other things worth checking, if the PCM change doesn't help?

I'm taking the car there and going to say I'm not taking it back until it works.

I got the car back today with the new PCM and immobilizer unit.

Now it works well. I'm not too excited yet, let's see how long it does work OK.

The PCM change was the only thing done this time, so there had to be something wrong with it.

Okay, the car started to misbehave again.

Two of the problems exist now:

1) The RPM goes too low (around 500) very fast, when the clutch pedal is pressed, and it takes a few seconds till it goes back to normal idle RPM.

2) It's impossible to change gears smoothly, related to the fast idle drop.

None of these problems exist when electrical load is not applied.

Before I got the car back from the mechanic, it had been in dry garage for two nights. The problems started again, when the car had been outside one night.

The voltage was measured at the mechanic's, it stayed between 13, 8V and 14, 2V with full electrical load.

Well, the problem is STILL the charging system.
The alternator was tested with the Mazda-tester, and the voltage dropped immediately to 12, 5V everytime when the gas pedal was released. The voltage was also tested without battery in between, it was only 9V.

Still the car gives the diagnostic code 1632 (SmartCharge system problem/Battery positive voltage too low)

The alternator (5 times), the PCM and the battery are replaced, as well as the alternator-to-battery positive cable. It has to be wiring somewhere? But where to look?