[Horneck]

I appreciate input from this forum as I am not getting further along solving my problem.
My Porsche 930 is refusing to rev over 3000RPM / 0.4 bar boost after sitting for 4 weeks in my garage. The car misfires when I exceed 3000 rpm. I can get it to rev past 4000 without load but have to be very careful with the throttle and only press it maybe 25%. If I press full throttle the misfire starts immediately. Between idle and 3000 RPM the car runs fine.
I assume it has something to do with the enrichment when the turbo starts to kick in. I have checked the fuel pumps and both work as well as the little connector at the mass airflow sensor. The turbo boost valve seem to be working as well.
What do you recommend to get the issue identified and corrected?