Odd Question for you guys...

[NeCrOmAnCeR]

Gasoline engines use throttles as mentioned. The computer can control idle speed using the "Idle Air Control" a small stepper motor which opens a small air passage allowing more air into the engine. The computer also uses various other sensors to monitor air flow into the engine at off-idle speeds to compute the correct ammount of fuel to add.

The majority of diesels you will come across are direct injection where the injector places the fuel directly into the cylinder. On the newer computer controlled types the duration and ammount of fuel are controlled by the computer to give the desired speed and power. On older engines, individual injectors are actuated with a camshaft lobe and ammount of fuel is controlled with a "rack" which rotated a sleeve in each injector that opened the drain port. Others use a central injection pump which does all the above and sends the pressurized fuel to each injector through steel lines. Like I said above most diesels are direct injection, there are a small ammount which use pre-combustion chambers in the head. The purpose is to cause greater "swirl" and allow more complete combustion. It was apparently found that the same thind could be accomplished other ways.

Hope this helps.