ABK does not start on petrol any more; on gas however already?!

Hello dear community, I’ve been having a problem with my Audi for a long time. And it doesn’t start on petrol anymore. But since a car gas system is installed, it’s all half as wild, because it actually only switches to petrol for start and then runs on LPG. And it also starts on LPG wonderfully. I still want to get it back in service, so I can also start on petrol again and drive as I like it I noticed when I’m on petrol while driving. switch, the engine continues to run. But only if I let it roll right after switching it to the accelerator pedal without kicking it. After that it runs a bit rough and then it goes. Sometimes, however, it doesn’t take any gas at all. I also noticed that I can start the engine right after I drove it and put it off again on petrol. Sometimes it runs on then, but sometimes it turns only briefly to about 1000-1500 rpm and then goes off again. Hope I could half Wegs understandably express…is not so easy to distinguish in the text between “give GAS” and “gas operation”. Greeting Funtiger83