GLC13B

I'm posting this for a friend of mine that has a 88 t2. The car starts right up and then idle's rough. The car drives fine until the 4k is reach and then she starts to stumble and turns off or idle really bad. Parts replaced were TPS, AFM, BAC Valve,spark plugs, Airflow controller and boost senor. Pollution pump was removed and replaced with a 91 Airflow controller. The black plug on the Airflow controller is being used. I'd appreciate any advice on this problem.