If the EGR valve is stuck open due to a carbon chip you will notice rough running at idle and low speeds when it is supposed to be closed, but it normally opens at higher speeds. You shouldn't feel it there. Throttle position sensor won't cause this either. At worst it will cause a hesitation or stumble on acceleration. It has the least say in how much fuel goes into the engine. The Engine Computer is a possibility if it fails to drive one of the injectors. GM did have a lot of computer trouble from the mid '80s through the late '90s.
If you can keep it acting up, most mechanics have scanners that have a test mode that allows you to fire each injector repeatedly. If it says the test is running but the injector isn't clicking or spraying fuel you can do some electrical tests to determine if there's no voltage getting to that injector or if the computer is not grounding the control wire to it.
Friday, September 6th, 2013 AT 8:25 PM