If you're looking for service to clean/flow-test fuel Porsche 928 fuel injectors they are a common type with service available in most large cities and on a national level. I used this search term for internet search and found many companies: company service test clean automobile fuel injectors
If you need service of the MAF, fuel and spark modules for the Porsche 928 I provide that service via my company Electronik Repair, Inc. My website is
www.electronikrepair.com ... drop me a note from the contact page if you have questions or need service.