MC2 misfires

[Dag Bøsterud]

I have a 1990 Audi 100 TQ Sport Exklusiv with the MC2-engine - vin L-117-450.
It has done about 142500 miles.

Over the last two years / 12500 miles I have replaced
all sensors, almost every vacuum/pressure hose thinkable, brand new Bosch injectors,
brand new TPS and the fuel filter. I have checked the different fuel pressures and they are to spesification. All ignition parts have also been replaced with OEM-parts within this time period.

I have installed an ecu chipped by MTM. With this ecu the car managed 0,6 (1,6 on the computer in the dashboard). I then installed a stiffer WG-spring. And now I've got the following problem:
If/when the car boosts 0,6 (1,6 in the computer/display in the dashboard) and goes over 4000-4500 rpm, the car misfires badly. I'm quite sure it's not fuel cut, because that feels like
knocking your head against the windscreen.

I've read fault codes, but the car reports "4444" = no fault found.

What could be wrong?

Any clues, hints or tips?

/Dag Bøsterud
Norway

1990 Audi 100 TQ Sport Quattro