i was about to say the same thing (the throttle position sensor) -- but i've had bad throttle position sensors not ever trigger a check engine light, so don't think that light has to be on for that sensor to be bad. you can check (or have a friend that knows how to work on electrical) the TPS with an voltmeter by finding the data wire (there are 3, one 5v+, one ground, & the third is data..... it's voltage changes from near zero, to 5v+ depending on how far the throttle is open) and with the key on in run (but the engine not started) monitor the voltage on that wire, as you slowly move the throttle completely thru it's motions several times. if at any point the voltage suddenly drops or swings high wildly, then recovers, move the throttle back the opposite direction and try to make it do it again. if you are able to get it to suddenly spike, then the position sensor is shot & needs replacing (usually about $20 to $30 at places like autozone, and it is just barely harder to change than a light bulb. simply unplug the electrical connector, remove the two screws, take the sensor off, put new sensor on, reinstall the two screws, plug the plug into the new sensor, you're done - takes a total of 5 minutes to do, and that's assuming you're having to learn english in order to read this first!)