Scion tc 2007 is running on low RPM?

I had my engine mount replaced by a mechanic who I trust, is very knowledgeable and always gives me a good deal. I had my engine mount replaced because in a test, the engine was moving, I also thought it had something to do with it shaking at Idle (In drive or park). But after everything was replaced, the engine was rock solid, but the car continued to shake. After a little investigating, my mechanic friend said my car was running low in the RPM at Idle,lower than normal. That's whats causing the car to shake he said. But he did say the car would be fine, but if I really wanted to check into it, I would have to get a scanner because for some reason my car doesn't have this certain switch that can switch it very easily. Getting the scanner though would be expensive, and unnecessary he said. But I wonder, has anyone else ran into this problem, and found a way to increase their Idle RPM, with the help of some sort of scanner?