Mruthunjaya U. Dhariwal, H. C. Dhariwal, Investigation of Control of Speed of Diesel Engines Using PID Governor, SAE Transactions, Vol. 109, SECTION 3: JOURNAL OF ENGINES (2000), pp. 222-237 ...

By the way, we’ve covered a PID library for Arduino before. While this post talks about temperature, PID control is used for everything from flight control to levitation.