Rugging on the Audi 80 B4

Hello, I have a question about an Audi 80 B4 Type 8C built in 1992 with 66kw/90PS: For some time the car has been jerking, but only while keeping a constant speed. When accelerating you don’t notice anything. Try so far: – Lamda probe plugged off to test if that makes the problem. – Distribution cap and cable changed. – Spark plugs renewed. – Carburettor flange (gummiflansch) changed. Unfortunately, still the problem with the jerking. Very bad to drive with the third 50km/h. It stutters right. Can someone tell me how to get the problem to the trick? Diagnosis device I have unfortunately none. in the ebay which do what? Thanks Klaus