So my tests on real engine was not so succesful:
1) My bench tests was using 30-40% PWM duty. In real life more than 75% needed. Because of this or another inductance of Audi 20V 5cyl n/a engines injectors heat stress was significant bigger. Things goes even worthier due 7Ohm IAC valve (what TVS diode do???). Here is additional aluminum wings as temporary solution:
2) Device last all break-in mileage and hard tuning sessions. But fails on second practice. On other region of my country. Thanks God it was best place to fail: diagnostic and repair make one of the best car electronics expert here. My focus was on thermo load. He see a too high base voltage during transients as a reason. TIP107 emitter base voltage is rated 5V only. So he put MOSFET IRFZ46N in place. Gate voltage can be +/-20V. It survive rally-sprint race day later.
3)Circuit produce lot of noise. LCD shows scrawl immediately after start. Same man suggest put additional capacitors between flyback pad and power GND inside VEMS unit. So wires to external flyback unit no more works as noise source. In addition I solder 0.1uF cap on LCD between supply pads and shorten both - LCD and keyboard wires inside ECU. It works perfectly!
For less heat power and safer fail effect I decide rewire my unit back to INJ + and replace zener to 36V. 36+18V(max allowable U
batt by VEMS)=54V It is 6V below INJ FETs maximum.
More tests ahead.
Gints