Clean Audi 90CS air intake system

I want to clean out the air intake system by myself... I want to clean out the part AFTER the Mass Air Flow (MAF) Sensor...
| Air Filter | MAF | T u b e | ----> This section here
So is there something I can spray AFTER the MAF, so I don't ruin it, and then run the engine... or do I really need to bring my car in? How much should I pay for an intake system cleaning? Can you use BG products with Audis?
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