You may have a faulty idle air control valve, if it is setting a check engine light you can go get a free diagnostic check and an auto zone.
〉 Answered on Mar 16th, 2008 by Amanda J. Pierce, MBA "AJ", Certified Mechanic, Project Coordinator; Primavera Scheduler at VIGOR Alaska Industrial Shipyard & BizzM3ch Solutions
Unfortunately, I cannot give you a definite answer to your question. The only way to properly diagnose symptoms like this is to bring the vehicle to a qualified technician and have him/her run some tests. It could be a very simple problem, like a faulty sensor or a loose wire, but there's no way of knowing for sure unless you have it looked at by a professional.
〉 Answered on Mar 16th, 2008 by Suzanne Grego, Technician at City of Philadelphia Fleet Management