C5 engine cut-off during drive

[vborovic]

Here's one for you with ideas, this exact car is not my specialty ... drove dad's car yesterday on cruise at 130 kmh, nothing unusual, then just for the fun of it (I don't drive it very often) decided to push it a bit faster, ans slowly accelerated to 160 kmh - when all of a sudden a small explosion rang in the engine compartment, a thud could be felt and the engine died, had to slowly pull to the side ... at the same time, the engine icon and the service light came on (no surprise there) and on the center screen 2 messages one after the other (engine management system faulty & depollution system faulty)

The car in question is a C5 facelift 2.0 petrol 136 bhp, at 118000 km, regularly serviced, no prior faults like this ... the car isn't driven much though, mostly short runs, daily 10-20 km max. I've restarted the engine, immediately after which I got the 2 mentioned messages, and slowly drove to the gas station, which was very conveniently near by (2 minutes). Stopped on the parking lot, gave the car a break, restarted 2-3 times, every time the two faults were immediately displayed after the engine turned on ... the engine is slightly noisier and rough then before, and at 6000 rpm you get an Impreza like backfire and black cloud out of the exhaust, with the engine getting a mighty kick to it (I doubt it is healthy for it at this point) ... after that, drove the car for 100 km, didn't pass 110 kmh, no issues, but the engine feels just a bit rougher.

The car did another 30 km today, went as far as 160 kmh, no apparent issues. Decided to hook it up to the Lexia, while testing at idle revs, the engine cut-off again, displaying only the depollution system faulty message. Some ideas that I've stumbled on the net as to what might be wrong with the car are the EGR valve, the air flow issue (some blockage) and the thermostat (the last one actually being reported by Lexia in the Ignition portion of the diagnostics as the permanent fault). I can drive the car to the Service on Monday, but if it is a stupid error, or something that could be fixed with no major efforts, I'd like to take it on myself.

Any takers on this?