If it stays running when you press the gas pedal, that suggests a possible problem with the idle speed motor. There is an air passage around the throttle blade that is opened by that motor to let more air in. That's how the computer controls idle speed. Your mechanic should be able to use his scanner to tell the Engine Computer to run the idle speed up and down to see if it's working. If it doesn't respond, that passage could be blocked with carbon. The motor could be defective too.
You should also get a nice "idle flare-up" to 1500 rpm when you start the engine, then it should come back down to around 800 rpm in a few seconds. If that occurs, the idle speed motor is working. If that doesn't occur, that can cause the engine to not start unless you hold the gas pedal down 1/8".
Be aware the idle speed motor doesn't do anything when you're driving except when coming to a stop. If the engine stalls at higher speeds, that's usually an electrical problem, typically with a sensor. Usually a diagnostic fault code will be set in memory and the Check Engine light will turn on. If there are no stored fault codes, a fuel supply problem would the best suspect.
Friday, June 1st, 2012 AT 6:50 AM