XK8, fun with electrics

I’m working on friends 1997 XK8 convertible. It’s giving a bit headache for me, stability control fail for starters. Car indicates it every time when powered. I’ve changed the battery and ABS module+pump for it. Nothing changes. OBD scanner is giving me strange readings, 36kph on front left wheel, 146kph on both rear wheels, this is when car is not moving. I can clear the values with OBD scanner, but they’ll come back when car is powered off and on again.
This is not all, when power is on and engine not running scanner gives strange values from ECM too. There is 65 points scanner can check on engine, and they all change frequently. For example, engine speed is constantly showing values 0 and 876 rpm. Every point that I check at ECM, does the same, showing two values, or when checking some switch, it is showing 1 or 0, and they all change in about 1 second.

The car has been put for 9 years in dry place, it is in good condition except the electrical issues.No mouse biting on wires or anything alarming. I’ve checked all the grounding places and all of the plugs for ECM/TCM/ABS modules and engine room fuse boxes. Of course all fuses too.

I’ve also checked all 4 abs sensors and I got good values from ABS plug with multimeter. Checked also the TCM plug from transmission end.

Oh, and is it normal when key is turned, no engine running, the throttle motor starts? It makes humming noise as long as powered off.

There’s probably a lot, that I forgot to mention. All sort of codes P1798, P1799, P1794 and so on, but I think it is because of something else funny happening in car’s electric system. Hope that someone could give some advice where to check next.

Hi if the battery is not above 100 amp hours this will cause all sorts of problems