my code on my pontiac grandam is p0507 for my service engine light. 1 mechanic

What is your question?

1 mechanic told me it was a carbon clean procedure that would cost 160-240. 2 friends from church recommended that I should first go get some injection fluid, then tomorrow morning go to their mechanic for another opinion. I maintain my car well--it has aLMOST 116,000 MILES. wHAT SHOULD i DO?