How to fix engine. Audi Coupe 2.0l 16v (ACE)(1993)?

I have a 1993 (K) Audi Coupe 2.0l 16v with an ACE engine code. She has cover 140k. In recent months she has been slightly difficult to start (both with hot and cold), but when running was fine! When i got her she was strong and ran well, then the slight starting prob and then getting spluttery and not very responsive (i also noticed she was using quite a bit of fuel)! I had a diagnostic done - this said lambda sensor (which i changed (for an aftermarket one)). To be honest this didn't make a difference and changed all other service parts which could affect the running- sparks, dizzy, HT etc. Things just kept getting worse and she became so spluttery and down on power that she was undrivable. The throttle just wouldn't respond and regardless of how far my foot was down nothing much was coming back - (it almost appeared to be struggling to breath!) Tick-over dropped to 200rpm (and sounded as if she was on just one or two cyclinders! IF i could get the revs up and keep them up the car was pretty much ok, but if they dropped then i would struggle to get it back. - Now i Can't really get her going and she's looking very sorry on my drive. The engine looks as if its been running alittle lean - (dry carbon desposits on sparks (no oil)). I believe the fault lays on the electronics - the fuel metring or even the newer lambda sensor (aftermarket) which is now cutting the engine?????????? can the lamda be bypassed (temporarily) to test the engine and get up and running (if so how?) Any other ideas?